Mammographic findings after breast cancer treatment with local excision and definitive irradiation

Following local excision and definitive irradiation of 163 breast cancers in 160 women, alterations in mammographic patterns were observed for up to 7 years. Skin thickening was observed in 96% of mammograms obtained within 1 year of completing therapy and was most pronounced in women treated with iridium implant, chemotherapy, or axillary dissection. In 76% of mammograms, alterations in the parenchymal pattern, including coarsening of stroma and increased breast density, were seen at 1 year. Neither skin nor parenchymal changes progressed after 1 year. Within 3 years of treatment the parenchymal density, which usually regressed, did not change in all patients. At 3 years skin thickness and the parenchymal pattern had returned to normal in less than 50% of the breasts of these women. Scars developed in approximately one-quarter of women. They were present on the initial post-treatment mammogram and remained unchanged on serial studies. Coarse, benign calcifications also developed in the breasts of about one-quarter of women. Microcalcifications developed in 11 breasts; biopsy specimens of six were benign. Benign microcalcifications may be related to therapy.     

Correlation between breast parenchymal patterns and mammographers' certainty of diagnosis

The density of breast tissue on a mammogram may affect radiologists' diagnostic decisions. To evaluate possible correlations among breast parenchymal pattern and diagnostic confidence, six radiologists classified 655 mammograms as N1, P1, P2, and DY, according to Wolfe's criteria. Evaluation of radiologists' confidence interpreting the mammograms (1 = absolutely certain, 2 = fairly certain, 3 = uncertain), shows a significant correlation between decreasing diagnostic certainty and increasing complexity of the mammographic breast parenchymal pattern. That readers are less confident in their interpretation of P2 and DY breast parenchymal patterns has implications for the operation of breast cancer screening programs.     

Sensitivity of MRI versus mammography for detecting foci of multifocal, multicentric breast cancer in Fatty and dense breasts using the whole-breast pathologic examination as a gold standard

OBJECTIVE: Our aim was to compare the effectiveness of mammography and MRI in the detection of multifocal, multicentric breast cancer. SUBJECTS AND METHODS: Ninety patients with planned mastectomies (nine bilateral) underwent mammography and dynamic gadolinium-enhanced MRI. Off-site reviewers aware of the entry criterion (planned mastectomy) evaluated both examinations for the presence of malignant foci, recording the density pattern on mammography. The gold standard was pathologic examination of the whole excised breast (slice thickness, 5 mm). RESULTS: Of 99 breasts, pathologic findings revealed 52 unifocal, 29 multifocal, and 18 multicentric cancers for a total of 188 malignant foci (158 invasive and 30 in situ). Overall sensitivity was 66% (124/188) for mammography and 81% (152/188) for MRI (p < 0.001); 72% (113/158) and 89% (140/158) for invasive foci (p < 0.001); and 37% (11/30) and 40% (12/30) for in situ foci (p > 0.05, not significant), respectively. Mammography and MRI missed 64 and 36 malignant foci, respectively, with median diameters of 8 and 5 mm (p = 0.033) and an invasive-noninvasive ratio of 2.4:1 (45:19) and 1.0:1 (18:18) (p = 0.043), respectively. The overall positive predictive value (PPV) was 76% (124/164) for mammography and 68% (152/222) for MRI (not significant). In breasts with an almost entirely fatty pattern, sensitivity was 75% for mammography and 80% for MRI (not significant), and the PPV was 73% and 65% (not significant), respectively. In breasts with fibroglandular or dense pattern, the sensitivity was 60% and 81% (p < 0.001), and the PPV was 78% and 71% (not significant), respectively. CONCLUSION: MRI was more sensitive than mammography for the detection of multiple malignant foci in fibroglandular or dense breasts. Mammography missed larger and more invasive cancer foci than MRI. A relatively low PPV was a problem for both techniques.     

Clinical performance of computer-assisted detection (CAD system in detecting carcinoma in breasts of different densities

OBJECTIVES: To determine the clinical performance of a computer-assisted detection (CAD) system in detecting carcinoma in breasts of different densities. MATERIALS AND METHODS: A total of 264 sets of bilateral screening mammograms taken in craniocaudal and medial-lateral oblique projections during the year 1997 were divided into four groups according to the BI-RADS density classification: fatty (pattern 1), scattered fibroglandular (pattern 2), heterogeneously dense (pattern 3) and extremely dense (pattern 4). Each group contained about 60% normal and 40% biopsy-proven cancer cases. Of the malignant cases, there were a mixture of mammographic findings including focal masses (<2.5 cm), asymmetrical density, architectural distortion or microcalcifications. Films with artefacts and obvious masses>2.5 cm were not included. The chosen cases were then digitized and analysed by the CAD system. Sensitivity was calculated as detection of cancer by at least one marker in at least one view. Specificity was calculated as the number of false-positive marks per image on normal cases. Statistical tests of significance were performed by using contingency tables and Chi square test. RESULTS: The CAD system detected 14 out of the total 15 cancer cases in totally fatty breasts with a sensitivity of 93.3% at a specificity of 1.3 false-positive marks per image. In breasts with scattered fibroglandular pattern, the sensitivity was 93.9% (31/33) and the specificity was 1.6 false-positive marks per image while in heterogeneously dense breasts, the sensitivity of the CAD system fell to 84.8% at a specificity of 1.6 false-positive marks per image. The sensitivity of the CAD system further dropped to 64.3% in markedly dense breasts while maintaining a specificity of 1.2 false-positive marks per image. The decrease in sensitivity in dense breast was found to be significant (p=0.046). CONCLUSION: The sensitivity of the CAD system deteriorated significantly as the density of the breast increased while the specificity of the system remained relatively constant.     

The mammographic parenchymal patterns of nulliparous women and women with a family history of breast cancer

One-hundred-and-thirteen mammograms of nulliparous women and 44 mammograms of women with a family history of breast cancer were graded according to Wolfe's parenchymal pattern classification. These were compared to 437 mammograms of women without these risk factors. Mammograms were read by two independent observers in order to evaluate inter- and intra-observer variation. The interobserver variation was reduced from 17% to 5% by combining high risk patterns (P2 and DY) and low risk patterns (N1 and P1). A significantly higher proportion of high risk patterns was found in nulliparous women compared to parous women (P less than 0.01). The proportion of high risk patterns decreased significantly with the number of children (P less than 0.01). Women with a family history of breast cancer had almost the same parenchymal patterns as women without a family history. In conclusion, while nulliparity and family history are recognized risk factors for developing breast cancer, only nulliparity would appear to influence the mammographic parenchymal pattern. This probably reflects the different mechanism by which the two factors affect breast tissue.     

Factors affecting the rate of false positive marks in CAD in full-field digital mammography

Objective

To assess the effect of breast density, fibroglandular tissue volume, and breast volume on the rate of false-positive marks of a computer-assisted detection software in digital mammography.

Materials and methods

222 patients with normal digital mammograms and a minimum follow-up of 22 months were retrospectively identified. MLO and CC views were analyzed using a CAD software with three operating points (‘specific’, ‘balanced’, ‘sensitive’). False-positive marks were recorded. Images were analyzed by a volumetric breast density assessment software, yielding estimates of percentage density, fibroglandular tissue volume, and breast volume. Statistical analysis was performed using the Mann–Whitney U-test, the t-test for independent samples and the Poisson regression model.

Results

Patients with high fibroglandular tissue volumes had a higher mean number of false-positive mass marks than patients with low fibroglandular tissue volumes (specific setting: 0.50 vs. 0.35, respectively; balanced setting: 0.70 vs. 0.40, respectively, p < 0.05; sensitive setting: 0.89 vs. 0.58, respectively, p < 0.05). Relative risk for a false-positive mass marker increased by 1.43 (p < 0.05), 1.63 (p < 0.001) and 1.50 (p < 0.01) per 100 ml of fibroglandular tissue for the specific, balanced and sensitive settings, respectively. No significant effects of percentage density or breast volume on the number or the relative risk of false-positive mass marks were observed.

Conclusion

The volume of fibroglandular tissue present, but not the percentage density of the breast, affected the specificity for masses of the CAD software investigated. This may have implications for improving the performance of CAD systems, as the specificity of CAD may be improved by adjusting the algorithm threshold depending on the volume of fibroglandular tissue present. Considering both factors, fibroglandular tissue volume and percentage density, independently, could improve overall CAD performance in subgroups of patients, e.g. those with small, dense breasts or large breasts with low density.     

Mammographic parenchymal patterns: value as a predictor of hormone dependency and survival in breast cancer

The relation between the parenchymal pattern of the breasts as demonstrated on a mammogram and the estrogen-receptor status of the primary tumor in 337 patients with operable invasive breast cancer has been studied. These factors have also been correlated with the response to endocrine therapy in 92 patients who subsequently developed secondary disease. It has been shown that patients with a DY pattern are more likely to develop tumors that are estrogen-receptor (ER) positive (p = 0.01). Patients with secondary disease who have a DY pattern are more likely to respond to endocrine therapy (p = 0.001). The DY pattern has been shown to be at least as good an indicator of the probability of response to endocrine therapy as the estrogen-receptor status, and a combination of the two factors better than either taken singly. In a series of 141 postmenopausal women, the DY pattern, as determined at the time of mastectomy, was associated with significantly improved survival (p = 0.001). Mammographic parenchymal pattern could form the basis for selecting patients for endocrine therapy where no estrogen-receptor assay is available.     

Impact of breast density on computer-aided detection for breast cancer

OBJECTIVE: Our aim was to determine whether breast density affects the performance of a computer-aided detection (CAD) system for the detection of breast cancer. MATERIALS AND METHODS: Nine hundred six sequential mammographically detected breast cancers and 147 normal screening mammograms from 18 facilities were classified by mammographic density. BI-RADS 1 and 2 density cases were classified as nondense breasts; BI-RADS 3 and 4 density cases were classified as dense breasts. Cancers were classified as either masses or microcalcifications. All mammograms from the cancer and normal cases were evaluated by the CAD system. The sensitivity and false-positive rates from CAD in dense and nondense breasts were evaluated and compared. RESULTS: Overall, 809 (89%) of 906 cancer cases were detected by CAD; 455/505 (90%) cancers in nondense breasts and 354/401 (88%) cancers in dense breasts were detected. CAD sensitivity was not affected by breast density (p=0.38). Across both breast density categories, 280/296 (95%) microcalcification cases and 529/610 (87%) mass cases were detected. One hundred fourteen (93%) of the 122 microcalcifications in nondense breasts and 166 (95%) of 174 microcalcifications in dense breasts were detected, showing that CAD sensitivity to microcalcifications is not dependent on breast density (p=0.46). Three hundred forty-one (89%) of 383 masses in nondense breasts, and 188 (83%) of 227 masses in dense breasts were detected-that is, CAD sensitivity to masses is affected by breast density (p=0.03). There were more false-positive marks on dense versus nondense mammograms (p=0.04). CONCLUSION: Breast density does not impact overall CAD detection of breast cancer. There is no statistically significant difference in breast cancer detection in dense and nondense breasts. However, the detection of breast cancer manifesting as masses is impacted by breast density. The false-positive rate is lower in nondense versus dense breasts. CAD may be particularly advantageous in patients with dense breasts, in which mammography is most challenging.     

The visibility of cancer on previous mammograms in retrospective review

AIM: To study how many tumours were visible in restrospect on mammograms originally reported as normal or benign in patients coming to surgery with proven breast cancer. The effect of making the pre--operative mammogram available was also assessed. MATERIALS AND METHODS: Three hundred and twenty initial mammograms of consecutive new breast cancer cases were analysed by a group of radiologists in the knowledge that all patients were later diagnosed with breast cancer. The films were read twice, first without and then with the later (pre-operative) mammograms available. The parenchymal density in the location of the tumour was classified as fatty, mixed or dense, and the tumours were classified as visible or not visible. The reasons for the invisibility of the tumour in the earlier examination were analysed. RESULTS: Fourteen per cent (45) of cancers were retrospectively visible in earlier mammograms without the pre-operative mammograms having been shown, and 29% (95) when pre-operative mammograms were shown. Breast parenchymal density decreased with age and the visibility of tumours increased with age. When considered simultaneously, the effect of age (over 55 vs under 55) was greater (OR = 2.9) than the effect of density (fatty vs others) (OR = 1.5). The most common reasons for non-detection were that the lesion was overlooked (55%), diagnosed as benign (33%) or was visible only in one projection (26%). Growing density was the most common (37%) feature of those lesions originally overlooked or regarded as benign. CONCLUSIONS: Tumours are commonly visible in retrospect, but few of them exhibit specific signs of cancer, and are recognized only if they grow or otherwise change. It is not possible to differentiate most of them from normal parenchymal densities. Saarenmaa, I. (2001). Clinical Radiology56, 40-43.     

Accuracy of assigned BI-RADS breast density category definitions

RATIONALE AND OBJECTIVES: Quantitative criteria for the Breast Imaging Reporting and Data System (BI-RADS) mammographic density categories have recently been defined as <25% dense for almost entirely fatty, 25%-50% dense for scattered fibroglandular densities, 51%-75% for heterogeneously dense, and >75% dense for the extremely dense category. The purpose of this study is to compare the range of percent mammographic densities with radiologist-assigned BI-RADS mammographic density categories and compare with the recently issued definitions. MATERIALS AND METHODS: In this study, 200 consecutive negative analog screening mammograms were assigned BI-RADS mammographic density categories independently by three radiologists blinded to the other readers' density assignment. Quantitative assessment of percent mammographic density was performed using previously validated software. RESULTS: All three readers agreed on BI-RADS mammographic density categories in 98 cases (49%), and two of three readers agreed in all 200 cases. Using two reader's consensus, median mammographic density (range) was 6.0% (0.5%-19.2%) for fatty, 14.8% (1.2%-52.7%) for scattered densities, 51.2% (15.9%-82.2%) for heterogeneously dense, and 78.4% (60.1%-87.9%) for extremely dense breasts. The percent mammographic density ranges for fatty and extremely dense breasts correlated well with BI-RADS definitions, whereas the ranges of densities in the scattered and heterogeneously dense categories were considerably broader. CONCLUSION: Fatty and extremely dense BI-RADS categories compare relatively well to defined criteria, and therefore may be helpful in breast cancer risk models. Scattered fibroglandular densities and heterogeneously dense categories have broad percent mammographic density ranges and may not function well in breast cancer risk models.     

Size, node status and grade of breast tumours: association with mammographic parenchymal patterns

A case-control study was designed to assess the association of mammographic parenchymal patterns with the risk of in-situ and invasive breast cancer. In addition, the relationship between tumour characteristics and mammographic patterns were also investigated. A total of 875 patients with breast cancer were selected and matched with 2601 controls. Mammographic parenchymal patterns of breast tissue were assessed according to Wolfe's classification, and statistical analysis was by conditional logistic regression. Relative to the N1 pattern, the odds ratios of having an invasive breast cancer associated with the P2 and DY patterns were 1.8 and 1.4, respectively. In addition, the odd ratios of having an invasive grade 3 breast cancer associated with the P2 and DY patterns were 2.8 and 3.9, respectively. Relative to the combined N1/P1 pattern, the odd ratios of having a breast cancer smaller than 14 mm, 15–29 mm, or larger than 30 mm associated with the combined high-risk P2/DY pattern (P2 + DY) were 1.2, 1.6, and 2.0, respectively. Finally, women with the P2/DY pattern were twice as likely to have a breast cancer which had already spread to the axillary nodes, compared to women with women with the N1/P1 pattern (odds ratios of 2.1 and 1.4, respectively). Our results confirm previous findings suggesting that mammographic parenchymal patterns may serve as indicators of risk for breast cancer. Our results also suggest that mammographic parenchymal patterns are associated with the stage at which breast cancer is detected. Received: 22 March 1999; Recieved after revision: 22 July 1999; Accepted: 27 July 1999     

Factors associated with mammographic pattern

Wolfe's criteria were assigned to mammograms of 202 women without breast cancer. Parity decreased the frequency of P2 patterns but not DY. P1 and N1 patterns apparently increased at the expense of P2 patterns. For every birth, the probability that a P2 pattern changed to P1 or N1 was roughly 7 or 8%. This effect was not limited to the first pregnancy, but also held for additional pregnancies. Low body weight was associated with dysplasia and prominent duct patterns. Reported declines of radiographic density with increasing age and/or menopause were confirmed. Ethnic group was unrelated to parenchymal pattern.     

Systematic ultrasonography in asymptomatic dense breasts

The purpose of this study was to evaluate the role of ultrasonography in breast cancer screening. 350 Bilateral ultrasound (US) were performed in 350 asymptomatic patients with dense breasts. 7.5, 10 And 13 MHz transducers were used (Esaote Biomedica, Italy). In 185/350 patients, sonograms were normal, abnormalities were seen in 165/350: cysts (117), solid nodules (44) and mixed echogenicity nodules (4). All but two solid lesions were benign. Both malignant lesions were invasive carcinomas, 18 and 11 mm in diameter. In retrospect, they were palpable, but not visible on mammograms. Retroprospective review revealed that 24.7 of cysts and 31% solid nodules could be seen on mammograms. In 4 patients with fibroadenomas, US made a false positive diagnosis of breast cancer. Follow-up was obtained for 6 to 18 months in 45% of patients. Routine supplemental US evaluation for patients with mammographically dense breasts does not appear to significantly contribute to the accuracy of the work-up.     

Incidental enhancing lesions found on MR imaging of the breast

OBJECTIVE: This study was undertaken to determine the frequency and significance of foci of enhancement having no corresponding mammographic or clinical abnormality that are encountered on MR imaging of the breast performed to evaluate mammograms with equivocal findings. MATERIALS AND METHODS: Reports from MR examinations of 103 patients who underwent MR imaging of the breast to evaluate questionable mammographic findings were retrospectively reviewed. We identified cases that had focal enhancing lesions without a corresponding mammographic or palpable abnormality. Clinical history, mammograms, MR images, and follow-up information were reviewed. RESULTS: Of the 103 patients, 30 (29%) had incidental foci of enhancement. These women were significantly younger, more often premenopausal, and more likely to have dense breasts than those who did not have incidental foci. Tissue confirmation of the incidental foci was available for seven patients, mammographic follow-up was available for a mean interval of 22 months for 22 patients, and no follow-up was available for one. Cancer at the incidental sites was diagnosed in one of the 30 patients with multiple foci. She was also shown to have cancer at the site originally questioned mammographically (index site). None of the remaining patients has had a diagnosis of malignancy at the incidental sites. CONCLUSION: Incidental enhancing foci are common in women undergoing breast MR imaging for questionable findings on mammography, occurring in 29% of our patients. Our results suggest that unless malignancy is diagnosed elsewhere in the breast, these incidental foci are unlikely to be malignant.     

Toluidine blue dye as a breast localization marker

We compared the efficacy of toluidine blue dye vs methylene blue as a visual marker for breast localizations in vitro and in vivo. In phase 1, the dyes were injected into 10 mastectomy specimens and allowed to diffuse for 24-48 hr. In phase 2, the breasts of four premastectomy patients were injected with the dyes and the dyes were allowed to diffuse for 3 3/4, 12, 24, and 47 hr before mastectomy. In phase 3, the breasts of 18 women in whom 20 breast localizations were performed before excisional biopsy were injected with methylene blue or toluidine blue up to 2 hr 10 min before the biopsy. All excised stained breast tissue was evaluated blindly. The amount of pain associated with injections of the dye was recorded. The 22 women in phases 2 and 3 had had mammograms before, and the parenchymal patterns had been classified according to Wolfe. In the patients injected 3 3/4, 12, 24, and 47 hr before mastectomy, more intense staining with less diffusibility was seen with toluidine blue than with methylene blue. In the 20 localization procedures before excisional biopsy, no difference in intensity of staining or radius of diffusion was seen between methylene blue and toluidine blue with maximal diffusion times of 2 hr 10 min. Breast parenchymal pattern did not correlate with stain intensity or diffusibility. The six patients in whom both methylene blue and toluidine blue were injected and the 18 patients in whom either dye was injected felt less discomfort at the time of injection of toluidine blue than of methylene blue. Our results suggest that toluidine blue causes less discomfort and produces a more intense stain with a smaller diffusion radius than methylene blue regardless of breast parenchymal pattern.     

Screen film vs full-field digital mammography: image quality,detectability and characterization of lesions

The objective of this study was to compare screen-film mammography (SFM) to full-field digital mammography (FFDM) regarding image quality as well as detectability and characterization of lesions using equivalent images of the same patient acquired with both systems. Two mammography units were used, one with a screen-film system (Senographe DMR) and the other with a digital detector (Senographe 2000D, both GEMS). Screen-film and digital mammograms were performed on 55 patients with cytologically or histologically proven tumors on the same day. Together with these, 75 digital mammograms of patients without tumor and the corresponding previous screen-film mammograms not older than 1.5 years were reviewed by three observers in a random order. Contrast, exposure, and the presence of artifacts were evaluated. Different details, such as the skin, the retromamillary region, and the parenchymal structures, were judged according to a three-point ranking scale. Finally, the detectability of microcalcifications and lesions were compared and correlated to histology. Image contrast was judged to be good in 76%, satisfactory in 20%, and unsatisfactory in 4% of screen-film mammograms. Digital mammograms were judged to be good in 99% and unsatisfactory in 1% of cases. Improper exposure of screen-film system occurred in 18% (10% overexposed and 8% underexposed). Digital mammograms were improperly exposed in 4% of all cases but were of acceptable quality after post-processing. Artifacts, most of them of no significance, were found in 78% of screen-film and in none of the digital mammograms. Different anatomical regions, such as the skin, the retromamillary region, and dense parenchymal areas, were better visualized in digital than in screen-film mammography. All malignant tumors were seen by the three radiologists; however, digital mammograms allowed a better characterization of these lesions to the Breast Imaging Reporting and Data System (BI-RADS;) [corrected] categories (FFDM better than SFM in 23 of 165 vs 9 of 165 judged cases in SFM). In conclusion, digital mammography offers a consistent, high image quality in combination with a better contrast and without artifacts. Lesion detection in digital images was equal to that in screen-film images; however, categorization of the lesions to the BI-RADS classification was slightly better.     

The relationship of "high risk" mammographic patterns to histological risk factors for development of cancer in the human breast

In the UK Trial for the Early Detection of Breast Cancer in Nottingham, 119 women were identified as having fibrocystic change with epithelial hyperplasia or in situ carcinoma. Their mammograms were classified according to Wolfe's criteria and the corresponding histology for each patient was classified for degrees of epithelial hyperplasia, atypia and in situ neoplasia using Page's criteria. A control population of patients presenting for breast screening was used to represent the general population. No correlation was found between the four mammographic Wolfe patterns, N1, P1, P2 and DY and histological evidence of epithelial hyperplasia, atypia or in situ carcinoma. A further study was carried out to determine histological features of Wolfe pattern, using radiological examination of resected breast tissue. The variation in Wolfe pattern was related to the distribution of fibrous and adipose tissue in the breast interlobular stroma and appeared to have no relationship to epithelial parenchymal content. This information does not support the hypothesis that radiographic densities of P2 and DY patterns correspond to high risk epithelial proliferation.     

Multifocal,multicentric, and contralateral breast cancers: bilateral whole-breast US in the preoperative evaluation of patients

PURPOSE: To evaluate the efficacy of preoperative bilateral whole-breast ultrasonography (US) in the detection of additional multifocal, multicentric, and contralateral cancers and the effect of US information on therapeutic decisions. MATERIALS AND METHODS: Two hundred one patients who had newly diagnosed breast cancer or who were suspected of having breast cancer underwent US examination of the ipsilateral and contralateral breasts with a 10-, 12-, or 13-MHz transducer. All solid lesions found at US alone were classified according to level of suspicion and were selected for biopsy. The US results were compared with mammographic findings. Sensitivity, specificity, and positive and negative predictive values were calculated. RESULTS: In ipsilateral breasts, US depicted 194 (97%) of 201 foci of invasive cancer and 52 (75%) of 69 foci of ductal carcinoma in situ (DCIS), whereas mammography and physical examination depicted 173 (86%) foci of invasive cancer and 56 (81%) foci of DCIS. In the contralateral breast, US depicted 11 (92%) of 12 foci of invasive cancer and four (57%) of seven foci of DCIS, whereas mammography and physical examination depicted six (50%) foci of invasive cancer and five (71%) foci of DCIS. Overall, US depicted mammographically and clinically unsuspected multifocal or multicentric cancers in 28 patients (14%) and contralateral cancer in eight patients (4%). On the basis of these US findings, therapy was correctly changed in 32 patients (16%). The sensitivity, specificity, and positive and negative predictive values of prospective classification of 77 solid lesions detected at US alone were 100% (36 of 36), 51% (21 of 41), 64% (36 of 56), and 100% (21 of 21), respectively. CONCLUSION: Bilateral whole-breast US complements mammography in the preoperative evaluation of patients with breast cancer.     

Decreasing rate of fatty involution at screening mammography

RATIONALE AND OBJECTIVES: This study was performed to document the perceived decrease in fatty involution at screening mammography during the past decade and evaluate the influence of hormone replacement therapy (HRT). MATERIALS AND METHODS: In December 1996, the mammograms of 261 consecutive screening patients with a comparison study obtained 5 years earlier were evaluated, and their breasts were categorized according to Breast Imaging Reporting and Data System categories for breast density. The women, aged 50-59 years, included 119 who had been receiving HRT for 0.25-15 years (mean, 3 years). From the files, 261 age-matched screening mammograms from 1986 were obtained; these patients also had comparison mammograms from 1981. Analysis of variance was used to determine differences between the 1980s group, the 1990s group receiving HRT, and the 1990s group not receiving HRT. Scheffé tests were used for post hoc comparisons. Stepwise regression analysis was used to evaluate the relative influence of age, decade, score of the first mammogram, and HRT. RESULTS: Breast density for the 1991 mammograms did not differ significantly from that in 1981 (P < .05). Initial breast density was the best predictor of final breast density in both decades (P < .001), regardless of HRT status. The change in breast density (toward fatty) over the 5-year interval in the 1980s (mean, 0.48) was significantly greater than that in both 1990s groups (mean for HRT group, 0.11; no HRT, 0.30; P < .05). CONCLUSION: These results confirm that breast density at screening mammography in the 1990s did not decrease with age at the same rate as in the 1980s, even in patients not receiving HRT.