AN ULTRASTRUCTURAL STUDY ON PERIDUCTAL ELASTOSIS IN HUMAN BREAST TUMORS

An ultrastructural study on elastosis of human breast tumors was made with special attention to the periductal elastosis and the cell responsible for elastic fiber formation. The elastosis was found prominently in scirrhous type of duct carcinoma. In the area of mild periductal elastosis, the elastic fibers with many microfibrils and a tiny central elastin were seen around the periductal fibroblasts which were characterized by attenuated cytoplasms with aggregates of microfilaments and slightly developed rough endoplasmic reticulum. With the thickening of the periductal wall, such an area was replaced by abundant mature elastic fibers with peripheral microfibrils and a few intervening ordinary fibroblasts. Therefore, it was suggested that the periductal fibroblasts which transformed into ordinary fibroblasts during the development of elastosis were primarily concerned with the elastic fiber formation. In the interlobular tissue in which both fibroblasts and myofibroblasts were present, the elastic fibers were larger than those of the periductal area and had less microfibrils in their periphery. The relationship between microfibrils and elastin during the early elastosis, maturation process of the elastic fibers, and cell modulation of the fibroblasts in the breast elastosis were discussed.     

Elastosis in neoplastic and non-neoplastic tissues from patients with mammary carcinoma

We studied a series of 585 patients with non-invasive or invasive ductal carcinoma in an attempt to assess the significance of elastosis. Elastosis in the neoplasm was recognized in 60% of the 549 patients with invasive ductal carcinoma. The grade of elastosis was correlated with both the histologic grade of differentiation and the 5-year survival rate. The incidence of elastosis, however, was 17% in the 36 patients with non-invasive ductal carcinoma and 38% in the 21 with invasive ductal carcinoma with a predominant intraductal component. The increased elastic tissue may therefore be influenced by the stromal infiltration of cancer cells. Mastectomy specimens from another series of 100 patients with mammary carcinoma were examined with regard to the volume of elastic tissue. Increased periductal elastic fibers were also identified in the non-neoplastic tissue, but the volume density was far less than in the neoplasm. A significant correlation was found between the increased amount of periductal elastic fibers in the non-neoplastic tissue, periductal elastosis of the neoplasm and an increase in parity. We propose that cancer cells in mammary carcinoma exert an inductive effect on mesenchymal cells for the synthesis of elastic material, under the basic condition of an increased amount of elastic fibers with an increase in parity.     

ELASTOSIS IN NEOPLASTIC and NON-NEOPLASTIC TISSUES FROM PATIENTS WITH MAMMARY CARCINOMA

We studied a series of 585 patients with non-invasive or invasive ductal carcinoma in an attempt to assess the significance of elastosis. Elastosis in the neoplasm was recognized in 60% of the 549 patients with invasive ductal carcinoma. The grade of elastosis was correlated with both the histologic grade of differentiation and the 5-year survival rate. The incidence of elastosis, however, was 17% in the 36 patients with non-invasive ductal carcinoma and 38% in the 21 with invasive ductal carcinoma with a predominant intraductal component. The increased elastic tissue may therefore be influenced by the stromal infiltration of cancer cells. Mastectomy specimens from another series of 100 patients with mammary carcinoma were examined with regard to the volume of elastic tissue. Increased periductal elastic fibers were also identified in the non-neoplastic tissue, but the volume density was far less than in the neoplasm. A significant correlation was found between the increased amount of periductal elastic fibers in the non-neoplastic tissue, periductal elastosis of the neoplasm and an increase in parity. We propose that cancer cells in mammary carcinoma exert an inductive effect on mesenchymal cells for the synthesis of elastic material, under the basic condition of an increased amount of elastic fibers with an increase in parity. ACTA PATHOL JPN 38: 1537-1546, 1988.     

Differential distribution of tenascin in the normal, hyperplastic, and neoplastic breast.

We studied by immunohistochemistry the distribution of tenascin with the monoclonal antibody 100EB2, and compared it with that of laminin in breast tissue samples from fetal, adult resting, lactating, and aging parenchyma, variants of fibrocystic disease, fibroadenomas, cystosarcoma phylloides, and ductal and lobular carcinomas. Monoclonal antibodies were applied to cryosections by the avidin-biotin-complex method; selected samples were studied by double immunofluorescence, and by Western blot analysis. In adult resting and aging breasts, tenascin immunoreactivity was noted in the periductal and periacinar stromal regions as thin irregular bands; in the lactating breast, broader periductal bands were observed. In these samples, laminin immunoreactivity was a single continuous line around ducts, acini, and vessels. In fetal breasts, tenascin appeared as thick periductal bands, whereas laminin remained as a delicate single line. In FCD, tenascin increased around ducts showing hyperplasia, papillomas and apocrine metaplasia, whereas laminin retained its delicate linear pattern. Similar patterns were seen in fibroadenomas and cystosarcoma phylloides with variable tenascin reactivity in the stroma beyond the ducts. Tenascin immunoreactivity was markedly increased around ducts containing in situ carcinoma appearing as broad bands, whereas that of laminin showed a linear, frequently discontinuous appearance. Prominent stromal tenascin immunoreactivity was seen in infiltrating ductal and lobular carcinomas, whereas laminin was virtually absent save for scattered lines. The abundance of tenascin in the carcinomatous stroma contrasted with its scarcity in the non-neoplastic stromal regions. By Western blotting, both chains of tenascin with molecular weights 250,000 and 180,000 were shown in ductal and lobular carcinomas as well as in normal breast. Tenascin immunoreactivity was noted in the periepithelial stromal regions of adult resting and aging breast ducts and acini. The amount of tenascin was moderately enhanced in certain physiologic conditions (fetal growth, gestation), as well as hyperplasias, dysplasias (fibrocystic disease) and benign tumors, whereas it was markedly enhanced in intraductal and infiltrating carcinomas. During fetal mammary development, adult physiologic and pathologic hyperplasias, and in carcinomas, the increasing tenascin reactivity contrasted with the stable or decreasing laminin reactivity.     

Pattern of distribution of intraductal and infiltrating ductal carcinoma: a three-dimensional study using serial coronal giant sections of the breast

The purpose of this study was to establish the 3-dimensional (3D) structure of the breast tissue and to study the distribution and relationship between the intraductal and infiltrating components of ductal carcinoma and other proliferative epithelial lesions of the breast. Thirty mastectomy specimens with infiltrating carcinoma less than 3.0 cm in diameter were serially cut in the coronal plane. Each giant section was divided into small sections for routine processing. Using Photoshop (Adobe) and PowerPoint (Microsoft) software programs, the routinely stained sections were scanned and assembled to reestablish complete giant sections of the breast and subsequently the 3D structure. Intraductal and infiltrating ductal carcinomas, epithelial hyperplasia with atypia, and marked epithelial hyperplasia without atypia were mostly confined to a single duct (27 cases), resulting in an increase in size of the involved breast segment. Three remaining cases included a case of Paget's disease with tumor appearing to spread from one duct system to another system through the epidermis and two cases with multiple separate foci of carcinomas located in different quadrants and accompanied by ductal spread in different lactiferous ducts. Both intraductal and infiltrating carcinomas were often located in the superficial segments (near the subcutaneous tissue) (28 cases). The infiltrating components were often located adjacent to area of pure intraductal carcinoma and were often peripheral (nearer the chest wall than the nipple). Intraductal carcinomas showed a "fanned out" pattern of distribution, frequently extended toward the nipple (with involvement of the nipple or subareolar tissue in 7 cases), and occasionally were seen in the breast tissue peripheral to the infiltrating carcinoma. Multiple ducts with intraductal carcinoma could be seen to be connected with each other with serial sections. However, in at least 6 cases, foci of intraductal carcinomas were separated from each other by segments of duct with benign epithelium. Breast carcinoma often arise from the breast segment close to the subcutaneous tissue. Infiltrating carcinoma lesser than 3.0 cm in diameter is usually located adjacent to the area of pure intraductal. The pattern of spread of intraductal carcinoma has a pyramid-like shape, with the summit toward and occasionally extending up to the nipple. These findings should be considered in the surgical strategy for segmental resections of breast carcinomas.     

Histopathology of benign non-palpable breast lesions identified by mammography.

Over four years the histological features of benign breast diseases, diagnosed after biopsy of non-palpable mammographic abnormalities, were reviewed and correlated with the mammographic appearances. The histological features were compared with those from all other benign biopsy specimens taken during the same period. The incidence of sclerosing adenosis and microcalcifications was considerably higher in the group of non-palpable mammographic lesions; fibrous disease of the breast and radial scar (infiltrating epitheliosis) were also more common. There was no difference in the incidence of epithelial hyperplasia between the two groups. Correlation with the mammographic appearances showed that microcalcification was most often associated with blunt duct adenosis and that stromal distortion or masses were most often caused by fibrous disease.     

Elastosis in lung carcinoma: Immunohistochemical, ultrastructural and clinical studies

Elastosis is the pathological finding of focal deposits of elastic fibers in abnormal amounts within tissue. It is well described in the case of infiltrating carcinoma of the breast, but elastosis in lung carcinoma has not been previously documented in detail. We investigated the characteristics of elastosis in lung carcinoma with light and electron microscopies, and immunohistochemistry for alpha-1-antitrypsin. A total of 184 surgically resected primary lung carcinomas were studied. Elastosis was detected in adenocarcinomas (85/106), squamous cell carcinomas (11/60) and adenosquamous carcinomas (5/7), but not in small-cell carcinomas (n = 4) or large-cell carcinomas (n = 5). The degree of elastosis in each case was divided into one of five grades, graded as 3+ to 1-. The score of elastosis was significantly higher in adenocarcinoma than that in squamous-cell carcinoma (P < 0.01). In the cases of adenocarcinoma, the mean score of elastosis in the well-differentiated type (WD n = 43) was higher than that in the moderately differentiated (MD) (n = 39; P = 0.012) and poorly differentiated (PD) types (n = 24; P < 0.01). The mean score of elastosis in MD adenocarcinoma was also higher than that in the PD type (P < 0.01). Light- and electron-microscopic analyses revealed that these elastic fibers in elastosis were composed of aggregates of thick mature and fine immature elastic fibers, and were positive for alpha-1-antitrypsin. It is suggested that both degraded elastic fibers and newly synthesized fibers are contained in the elastosis of lung carcinoma. Although no significant evidence was detected to suggest any correlation between elastosis and the degree of tumor invasion, the survival curves of adenocarcinomas with elastosis showed a significantly improved prognosis than of those without elastosis in the cases of stages IA and IB (n = 52; P = 0.026).     

Elastosis in lung carcinoma: immunohistochemical, ultrastructural and clinical studies

Elastosis is the pathological finding of focal deposits of elastic fibers in abnormal amounts within tissue. It is well described in the case of infiltrating carcinoma of the breast, but elastosis in lung carcinoma has not been previously documented in detail. We investigated the characteristics of elastosis in lung carcinoma with light and electron microscopies, and immunohistochemistry for alpha-1-antitrypsin. A total of 184 surgically resected primary lung carcinomas were studied. Elastosis was detected in adenocarcinomas (85/106), squamous cell carcinomas (11/60) and adenosquamous carcinomas (5/7), but not in small-cell carcinomas (n = 4) or large-cell carcinomas (n = 5). The degree of elastosis in each case was divided into one of five grades, graded as 3+ to 1-. The score of elastosis was significantly higher in adenocarcinoma than that in squamous-cell carcinoma (P<0.01). In the cases of adenocarcinoma, the mean score of elastosis in the well-differentiated type (WD n = 43) was higher than that in the moderately differentiated (MD) (n = 39; P = 0.012) and poorly differentiated (PD) types (n = 24; P<0.01). The mean score of elastosis in MD adenocarcinoma was also higher than that in the PD type (P<0.01). Light- and electron-microscopic analyses revealed that these elastic fibers in elastosis were composed of aggregates of thick mature and fine immature elastic fibers, and were positive for alpha-1-antitrypsin. It is suggested that both degraded elastic fibers and newly synthesized fibers are contained in the elastosis of lung carcinoma. Although no significant evidence was detected to suggest any correlation between elastosis and the degree of tumor invasion, the survival curves of adenocarcinomas with elastosis showed a significantly improved prognosis than of those without elastosis in the cases of stages IA and IB (n = 52; P = 0.026).     

Expression of CD44s, CD44v6, and hyaluronan across the spectrum of normal-hyperplasia-carcinoma in breast.

BACKGROUND: The interaction between transmembrane receptors on epithelial tumor cells and the surrounding extracellular matrix molecules is important in tumor progression and metastasis. This interaction is best exemplified by the relationship of the receptor CD44 and the extracellular matrix component hyaluronan (HA). This study seeks to evaluate the expression and the correlation of CD44s, CD44v6, and HA in normal, hyperplastic, and malignant breast epithelium and stroma. MATERIALS AND METHODS: Archival paraffin-embedded tissue from cases of normal breast tissue (n=10), intraductal hyperplasia without atypia (n=13), ductal carcinoma in situ (DCIS) (n=24), stage I infiltrating ductal carcinoma (n=28), stage II infiltrating ductal carcinoma (n=31), and their corresponding positive lymph nodes were retrieved from the surgical pathology files. Tissue sections were evaluated for the expression of CD44s, CD44v6, and HA in the epithelial and stromal cells by immunohistochemistry. RESULTS: Ductal epithelial cells and myoepithelial cells expressed CD44s in all cases of normal and benign breast tissue. The expression of CD44s in breast epithelium progressively decreased with increasing deviation from normal histology: 83% in DCIS, 46% in stage I ductal carcinoma and 26% in stage II ductal carcinoma. The reverse trend was observed for CD44v6 in ductal epithelium: 0% in normal breast, 15% in intraductal hyperplasia, 100% in DCIS, 82% in stage I infiltrating ductal carcinoma, 94% in stage II carcinoma, and 100% of metastatic carcinoma in the lymph nodes. HA was noted exclusively in the stroma but not in the epithelial cells. HA was faintly expressed in the intralobular stroma of normal breast tissue, confined to a narrow faint band adjacent to intraductal hyperplasia and localized to a broad well-defined band around DCIS. Stromal HA staining was more diffuse and intense in infiltrating carcinomas and was particularly pronounced surrounding the metastatic deposits in lymph nodes. CONCLUSIONS: This study demonstrates decreased expression of CD44s accompanied by increased expression of CD44v6 and increased stromal HA in breast cancer. These findings suggest that CD44s, CD44v6, and HA play complementary roles in the development and progression of breast cancer.     

Malignant and benign papillary lesions of the breast

This presentation describes criteria that we found most helpful in classifying the various proliferative changes of the breast and in separating papillary carcinoma from other benign papillary lesions. The criteria we used are easily understood and extremely reproducible.The true incidence of benign proliferative changes in fibrocystic disease and the significance of these lesions in later development of cancer were determined by studying 200 randomly selected cases of fibrocystic disease seen at least 10 years earlier. Of the 200 cases of fibrocystic disease, 40 showed intraductal papillomatosis or terminal duct hyperplasia. None of the patients with benign proliferative lesions for whom we have complete follow-up data (up to 14 years) developed cancer.In order to determine the type of proliferating cells in papillary carcinoma and benign proliferative lesions, some of the recently encountered cases were studied by transmission and scanning electron microscopy and histochemistry. Our ultrastructural and histochemical study suggests that both epithelial and myoepithelial cells participate in papillary lesions of the breast.     

Elastosis in the normal aging breast. A histopathologic study of 140 cases.

The incidence and pattern of elastosis of the breast was studied in tissue specimens taken at autopsy from 140 women with clinically normal breasts, ranging in age from 19 through 101 years. Elastosis, presence of excess elastic fibers, while less common in younger women, may be found in nearly half of all women over age 50 years with no breast disease. Elastosis occurs in three sites: diffusely in the stroma, around vessels, and around ducts. In the first two sites, it bears little relationship to age, while periductal elastic tissue appears to accumulate with age, probably reflecting parity, until about age 50 years. Thereafter, it is found at a more or less constant incidence and degree. While it may be associated with breast cancer, periductal elastosis by itself is not a cause for concern. Marked perivascular elastosis is, however, uncommon at any age, and its presence should suggest a special search for carcinoma, if not already evident.     

Benign breast lesions with malignant clinical and mammographic presentations

Nine cases of benign breast disease in which mammograms had been false-positive were collected at Northwestern Memorial Hospital. In all but one case the patients had presented initially with questionable masses that required biopsies with requests for frozen section diagnoses. Included in the study were three cases of indurative mastopathy, three cases of fibrocystic disease with sclerosing adenosis, and one case each of sclerosing papillary proliferation, infarcted intraductal papilloma, and fat necrosis with foreign body giant cell reaction. The mammographic and histologic findings for all cases were reviewed. Indurative mastopathy is a poorly known entity with radiologic features highly suggestive of malignancy. As described previously (Cancer 47:561, 1981), the lesion consists of a central nidus of elastosis with irregular projections radiating into the adjacent breast tissue. Peripheral areas of the infarcted papilloma and sclerosing papillary proliferation could be confused with infiltrating carcinoma in frozen sections. Familiarity of pathologists with these lesions is essential for avoiding the overdiagnosis of carcinoma.     

A comparison of the pattern of cathepsin-D expression in fibroadenoma, fibrocystic disease, preinvasive and invasive ductal breast carcinoma.

In the metastatic process, proteolytic enzymes play an important role in mediating the passage of cancer cells through the basement membrane and extracellular matrix. We have compared cathepsin-D (CD) expression in a range of benign and malignant breast lesions so as to investigate its role in breast cancer progression. One hundred and sixty-two breast samples, comprising 18 fibroadenomas, 22 fibrocystic disease, 96 invasive ductal carcinoma and 26 lesions with intraductal carcinoma components, were evaluated for CD expression by the standard avidin-biotin-immunoperoxidase complex method on formalin-fixed, paraffin-embedded histological sections using a commercial antibody against human cathepsin-D. Of the invasive ductal carcinomas, 61.5% showed stromal cell CD positivity, whereas 48.9% expressed CD positivity in neoplastic cells. There was significant correlation between neoplastic cell and stromal CD positivity. The prevalences of CD positivity in both neoplastic and stromal cell components were significantly higher (P < 0.05 and P < 0.01, respectively) in histological grade III tumors compared to grades I and II carcinomas. CD expression by either neoplastic or stromal cells did not show significant correlation with patient age and tumor size. Only 15% of intraductal carcinomas were CD positive and expression was limited to neoplastic cells. Neither epithelial nor stromal cells in fibrocystic lesions and fibroadenomas were CD positive, but a weak to moderate positivity was observed within myoepithelial cells in mammary ducts. These findings provide insights into the mechanism whereby tumors with high histological grade mediate invasion into tissue. The role of stromal cells in tumor progression and the means of their recruitment deserve further study.     

Abnormal Elastic Fibers in Elastosis of Breast Carcinoma UItrastructuraI and ImmunohistochemicaI Studies

Elastosis in benign and malignant breast lesions was studied by light microscopic immunohistochemistry for elastin and by electron microscopy. Upon immunohistochemical examination for elastin, elastosis, particularly in scirrhous-type ductal carcinoma, showed two characteristic staining patterns: fibrously and intensely stained elastic fibers and evenly stained elastic masses. Elastic fibers showing increased fibrous staining occurred mainly in the stromal areas, and were considered to be newly formed because they consisted of tannic acid-positive amorphous components and abundant microfibrils. Evenly stained elastic masses were observed mainly in the periductal areas and showed less intense stainability. These masses consisted of numerous fine amorphous components with plentiful microfibrils. In some regions within these masses, there were condensed accumulations of irregularly arranged small amorphous components associated with only a few microfibrils. These amorphous components had an ill-defined outline and were occasionally associated with spiralling collagen fibrils and cell debris. On the basis of these findings, the periductal evenly stained elastic masses were thought to be formed by excessive production of elastic fibers and degradation of pre-existing and newly formed elastic fibers. Acta Pathol Jpn 39: 245–253, 1989.     

Histopathological study on branches of the pancreatic duct in obstructive pancreatic disorders

Branches of the pancreatic duct in obstructive pancreatic disorders were studied histopathologically. Obstructive pancreatic disorders were observed in 25 out of 32 patients with pancreatic carcinoma. The main pancreatic duct was dilated in all 25 cases. Luminal conditions in the branches of the pancreatic duct were divided as follows: dilated, obstructed and unchanged. The dilated duct was found in all 25 cases and showed mainly cystic dilatation with flat epithelia. The obstructed duct was found in 10 cases and revealed granulation tissue in the lumen, disappearance of epithelia and increase in the number of elastic fibers in the periductal space. The pancreatic tissue distal to the tumor frequently showed isolated islets of Langerhans with elastosis. Morphogenesis of elastosis was interpreted as follows: during the process of shortening or disappearance of the duct, elastic fibers increased in number and remained in the fibrous tissue. Hence, the elastosis was considered to be a remnant in which the pancreatic duct had once existed. Therefore, the branches of the pancreatic duct in obstructive pancreatic disorder were classified into four types as follows: dilated, obstructed, remnant and unchanged.     

乳腺增生病组织学分类及其与乳腺癌关系的研究

以纤维组织增生为指标将乳腺增生病分成小叶增生、纤维腺病和纤维硬化三个组织类型，每型又有单纯性或复合性病变，后者含导管上皮细胞不典型增生等。增生病变的进展与年龄增长相关。纤维硬化型患者年龄与癌周伴乳腺增生病的患者年龄相近。三种类型的增生病增殖细胞核抗原阳性表达水平逐步递增；纤维硬化型增殖细胞核抗原阳性表达与癌平行。纤维硬化型导管和不典型增生的导管管周肌上皮和基底膜扭曲、断裂、不完整绕管的改变提示在临床上应密切随访。     

Montgomery's areolar tubercle. A light microscopic study

Conflicting impressions regarding the anatomy of Montgomery's areolar tubercle exist. Twelve modified radical mastectomy specimens provided 1,536 serial sections of areolar tubercles. In 34 of 35 tubercles (97%), a mammary lactiferous duct was associated with a sebaceous apparatus. This lactiferous duct ascended from deeper mammary parenchyma and entered the sebaceous gland. Histopathologic changes identified included featured of fibrocystic disease, atypical intraductal hyperplasia, and carcinoma in situ. Because the areolar tubercle has two components, a sebaceous gland and a mammary duct arising from deeper breast parenchyma, diseases of the breast may also involve the areola independent of papilla-nipple involvement. Areolar preservation may best be used with the knowledge that diseases underlying the areola may also involve the areola.     

Localization of a membrane glycoprotein in benign fibrocystic disease and infiltrating duct carcinomas of the human breast with the use of a monoclonal antibody to guinea pig milk fat globule membrane.

With monoclonal antibody D-274, raised against guinea pig milk fat globule membrane, the distribution of mucinlike glycoproteins of Mrs greater than or equal to 400,000 was determined in benign fibrocystic disease and infiltrating duct carcinoma of the human breast. These glycoproteins, called collectively PAS-I, were detected in 19 out of 20 cases of benign fibrocystic disease and in at least 26 out of 47 cases of infiltrating duct carcinoma. PAS-I was concentrated on luminal surfaces of ducts and alveoli in morphologically differentiated regions of the tumors. In areas where the glandular nature of the tissue was less evident in infiltrating duct carcinoma, the PAS-I determinant recognized by antibody D-274 was present on irregular luminal surfaces and in the cytoplasm. There was a negative correlation between the short-term recurrence (less than 2 years) of infiltrating duct carcinoma and the detection of strong positive staining with antibody D-274. The results are discussed with reference to recent studies on PAS-I in human breast tissue using monoclonal antibodies raised against human milk fat globule membrane.     

Duct elastosis in infiltrating carcinoma of the breast

Duct elastosis was studied in 219 patients subjected to radical mastectomy for infiltrating carcinoma of the breast, with a 10-year follow-up. Duct elastosis is a frequent finding in infiltrating breast cancer (65% of our cases). It develops in tumors of all three grades of malignancy, but it is more frequent in tumors of low grade malignancy (76% and 74% in grades I and II, respectively, and 47% in grade III tumors). In spite of their greater incidence in low malignancy tumors, the elastotic cases have a greater metastatic ratio than the non-elastotic cases (66% vs 45%). The elastotic cases also contain a significantly greater proportion of scirrhous tumors than the non-elastotic cases (86% vs. 32%). Duct elastosis and scirrhous reaction are two processes which develop in parallel, but are not related etiologically. They seem to be correlated with more advanced stages of the neoplastic disease. The influence of duct elastosis upon the ten year survival of the patients is unfavorable. this influence is not direct, and it is particularly evident in the metastatic cases. It seems to be related to the greater duration of the neoplastic disease and to the slow clinical course of tumors of low degree of malignancy.     

Feulgen DNA content and mitotic activity in proliferative breast disease. A comparison with ductal carcinoma in situ

Nuclear Feulgen DNA content was measured by cytophotometry and the number of mitoses per 40 high power fields was determined in hyperplastic and atypical hyperplastic lesions of fibrocystic disease in 18 patients, in ductal carcinoma in situ in 14 patients and in ductal carcinoma in situ associated with infiltrating carcinoma in 11 patients. These parameters were also investigated in the hyperplastic lesions accompanying ductal carcinoma in situ and ductal carcinoma in situ associated with infiltrating carcinoma. The nuclear Feulgen DNA content could not discriminate between atypical hyperplasia and ductal carcinoma in situ. Although differences in the mitotic count between hyperplastic and atypical breast lesions were not statistically significant, there was a statistically significant greater mitotic count in ductal carcinoma in situ alone or associated with infiltrating carcinoma. These findings suggest that the mitotic count is useful for the differential diagnosis between atypical hyperplasia and ductal carcinoma in situ. In addition, hyperplastic lesions associated with ductal carcinoma in situ, with or without infiltrating carcinoma, exhibited a statistically significant higher mitotic count than those in benign fibrocystic disease. Hyperplastic breast lesions exhibiting high mitotic counts may indicate the presence of a neighbouring ductal malignancy and suggest an increased proliferative activity in breast tissue in the neighbourhood of malignancy.