Ras oncogene expression and DNA content in plasma cell dyscrasias: a flow cytofluorimetric study

Using bivariate flow cytofluorometry, we have determined the nuclear DNA distribution and the expression of the p21 protein (coded by the Ha-ras oncogene) in the bone marrow (BM) cells of five solid tumour patients having histologically normal BM and in those of 57 patients with plasma cell dyscrasia (28 with monoclonal gammopathies of undertermined significance, MGUS, and 29 with multiple myeloma, MM). All normal and MGUS and 21/29 (72.4%) MM BM had diploid modal DNA content and 8/29 (27.6%) MM BM had both diploid and hyperdiploid cell populations. In normal and MGUS BM, the level of the p21 oncoprotein was low and uniform in all G0/G1, S and G2 cells (median fluorescence values in arbitrary units were 6.1 and 7.5, respectively). The level of p21 was increased both in different aliquots of G0/G1 cells and in the S and G2 cells in diploid MM (median value for G0/G1 cells was 20), and especially in MM with hyperdiploid clones (median value for hyperdiploid cells was 40.5, P less than 0.005 with respect to normal and MGUS BM and less than 0.005 with respect to diploid MM BM). The p21 expression was greater in patients with advanced (stage III) than in earlier MM (stages I + II) (P less than 0.005), and it was directly related to the BMPC infiltration (r = 0.7; P less than 0.005). Since p21 expression is greater in MM than in both normal and MGUS BM, Ha-ras could be involved in the malignant plasma cell transformation that distinguishes MM from MGUS.     

Flow cytometric analysis of pituitary tumors. Correlation of nuclear antigen p105 and DNA content with clinical behavior

Flow cytometric quantitation of the proliferation-associated nuclear antigen p105 and DNA content was performed on nuclear suspensions from 12 paraffin-embedded pituitary macroadenomas and one pituitary carcinoma and correlated with clinical outcome. Median follow-up was 41 months (range, 33 to 48 months). Three of the 13 tumors (23%) had an identifiable aneuploid peak. Of the four tumors that recurred or metastasized, only one was aneuploid. Nuclear antigen analysis of all diploid tumors showed enhanced p105 expression in G2M phase cells compared to G0G1 cells. The G2M/G0G1 fluorescence ratio for p105 was consistently higher (P less than 0.05) for the three diploid tumors that recurred (median, 1.32 arbitrary fluorescence units; range, 1.27 to 1.80) than for the seven nonrecurrent diploid tumors (median, 1.20 arbitrary fluorescent units; range 1.14 to 1.22). These findings indicate a low incidence of DNA aneuploidy among pituitary tumors and suggest that for diploid adenomas, measurement of p105 may provide information useful in predicting prognosis and directing postoperative adjuvant therapy.     

DNA flow analysis of soft tissue tumors

The cellular DNA content of 81 soft tissue tumors was determined by means of flow cytometry and related to conventional histologic classification of the same tumors. Comparison of histologic and cytometric analysis showed that all 23 benign tumors were diploid (normal DNA content), whereas the malignant group included both diploid and aneuploid (abnormal DNA content) lesions. There appeared to be a relationship between tumor grade and ploidy level in that 92% of Grade II, 28% of Grade III, and 11% of Grade IV lesions were diploid. Cell distribution analysis, feasible in 51 cases, disclosed that diploid lesions had a low proportion of S and G2 + M cells and most aneuploid lesions a high proportion, indicating a relationship between ploidy level and proliferative activity. The current study shows that solid mesenchymal tumors may be analyzed by DNA flow cytometry. Regardless of histogenetic type, it appears that benign and low-grade tumors are diploid and high-grade tumors, in general, are aneuploid. As to exceptions, DNA analysis may prove to give information beyond that obtained by subjective histologic interpretation. Thus, adequate follow-up might show that high-grade lesions with a diploid DNA content are associated with a better prognosis than expected from histologic classification.     

Flow cytometric analysis of DNA and cell proliferation in ovarian tumors

DNA content in tumor cells from 50 patients with ovarian tumors was analysed by flow cytometry (FCM). Solid tissue samples were processed to obtain monodispersed cells. Staining for DNA analysis was achieved with ethidium bromide and mithramycin. Peripheral blood lymphocytes were used as reference diploid cell population. All benign ovarian tumors exhibited only diploid cells. DNA aneuploid cell lines were found 66.6% of serous carcinomas and in 80% of malignant granulosa cell tumors. The S-phase fraction of DNA diploid cells in benign ovarian tumors (S = 2.4 +/- 1.2%) was smaller than those of malignant tumors (S = 8.2 +/- 5.2%). DNA aneuploid cell populations in serous carcinomas display a higher S-phase fraction (S = 19.2 +/- 9.3%) than DNA diploid cells (S = 11.7 +/- 3.2%). No major differences were obtained between primary ovarian tumors and their metastases, as far as degree of aneuploidy and S-phase fraction are concerned. A high degree of correlation was established between the grade of differentiation of ovarian tumors and the DNA ploidy abnormalities.     

Flow cytometrically determined DNA content of breast carcinoma and benign lesions: correlations with histopathological parameters

The relative DNA content of cellular samples from 54 patients affected by breast carcinomas and 20 affected by benign breast lesions (including 11 fibroadenomas) was measured by flow cytometry. All normal tissue samples and 17/20 (85%) specimens from benign lesions exhibited a cytometrically diploid DNA distribution, 3/20 (15%) benign lesions an abnormal DNA content, and 35/54 (65%) carcinomas at least one aneuploid cell subpopulation. Furthermore, 9/54 (17%) tumors were characterized by the presence of more than one aneuploid cell subpopulation. The results also indicate that flow cytometry can be used to recognize lymph nodes infiltrated by aneuploid cells. Statistically significant correlations were evidenced between the occurrence of aneuploidy or the ploidy level measured as DNA index and the nodal infiltration status. The percentage of S cells can also be extracted from DNA content distribution histograms. Statistically significant differences (p less than 0.01) were also observed for the percentage of S cells between normal tissues (6.2 +/- 3.2 SD) and benign lesions (11.1 +/- 6.6 SD), normal tissues (6.2 +/- 3.2 SD) and aneuploid tumors (19.7 +/- 10.3 SD), benign lesions (11.1 +/- 6.6 SD) and aneuploid tumors (19.7 +/- 10.3 SD), and diploid (7.9 +/- 4.0 SD) and aneuploid tumors (19.7 +/- 10.3 SD).     

Flow DNA analysis of primary bone tumors. Relationship between cellular DNA content and histopathologic classification

The cellular DNA content of 15 benign and 34 malignant primary bone tumors was analyzed by means of flow cytophotometry. All benign tumors except one of questionable histologic type exhibited a normal DNA content (diploid), whereas 23 of 34 malignant tumors showed an abnormal DNA content (aneuploid). Closer analysis revealed that all supposedly highly malignant tumors, i.e., 16 osteosarcomas and 1 Ewing sarcoma were aneuploid, while 8 of 13 chondrosarcomas, 2 periosteal osteosarcomas, and 1 of 2 adamantinomas were diploid. Interestingly, these diploid malignant tumors represent tumor entities which are known to include variants of low-grade malignancy. Cell distribution analysis showed that the aneuploid tumors exhibited a higher proportion of S-phase and G2 + M cells than the diploid tumors, indicating differences in proliferative activity. However, no significant difference in this respect could be demonstrated between diploid benign and diploid malignant tumors. The current study clearly shows that flow DNA cytophotometry can be applied to most primary bone tumors despite a substantial content of hard tissue. The results also indicate that DNA determinations as an adjunct to conventional histopathologic assessment may provide objective clinically relevant information with respect to the degree of malignancy. Thus, regardless of histogenetic origin, it appears that benign bone tumors as well as malignant bone tumors of low-grade malignancy in general, are diploid, whereas highly malignant bone tumors in general are aneuploid.     

Prognostic significance of DNA image cytometry in libyan breast cancer

Background: We evaluated the relation of nuclear DNA content and clinicopathological features and prognosis in primary breast cancer of female Libyan patients with variable stage and grade and different treatment regimes. Patients and Methods: Histological samples from 104 patients of breast carcinoma were retrospectively studied by computerized nuclear DNA cytometry. Isolated nuclei from paraffin sections were stained with Feulgen stain and DNA was measured using a computer-assisted image analysis cytometry system. In each case, 200 nuclei were measured and the DNA histograms, S phase fraction (SPF) and number of cells above 5c and 9c were determined. We applied different approaches in the analysis of DNA to compare the DNA histograms with different clinicopathological features and survival. Results: The mean of DNA ploidy mode for all tumors was 3.43; 82.7% of tumors were aneuploid and 17.3% were diploid. The median SPF was 3.5% for DNA diploid and 13.5% for DNA aneuploid tumors. DNA aneuploid tumors and high SPF were associated with advanced stage, distant metastasis, high histological grade and lymph node involvement. The SPF was also associated with large tumor size and with younger patients (<50 years). In the overall population (median follow-up 51 months), patients with aneuploid DNA histograms and high SPF values had shorter survival times than those with diploid DNA histograms and low SPF values (p = 0.001, p < 0.0001, respectively). Also, short survival was associated with a multiploid DNA histogram and with DNA aneuploid cells ≥5 cells (p < 0.0001, p = 0.001, respectively). In a Cox multivariate analysis, DNA ploidy (p = 0.010), age (p = 0.038) and clinical stage (p = 0.001) were independent predictors of overall survival, and DNA ploidy (p = 0.018) and clinical stage (p = 0.001) also proved to be independent predictors of disease-specific survival. The SPF cutoff point of 11% might be applied to separate patients into good and poor prognosis groups. Conclusions: DNA image cytometry with careful analysis of the histograms may provide valuable prognostic information in Libyan breast cancer, with potential clinical implications in patient management, particularly in predicting the patients at high risk for metastasis and recurrence who should be considered as candidates for combined adjuvant therapy.     

DNA aneuploidy and cell proliferation in breast tumors

The cellular DNA content of 30 benign and 180 malignant breast tumors was analyzed by means of flow cytometry (FCM). All benign tumors exhibited a normal DNA content (diploid), whereas 65% of the malignant tumors showed an abnormal DNA content (aneuploid). The ploidy distribution of malignant tumors was bimodal with an increasing frequency near diploid DNA index (DI), and a second group had a DI ranging from triploid to tetraploid. In estimating the degree of malignancy eight independent histomorphologic and cytologic criteria were introduced. A good correlation was observed between DNA content abnormalities and the grade of differentiation of breast carcinomas. The percentage of S-phase cells of DNA aneuploid cell lines was significantly higher than in the diploid ones. The highly differentiated breast carcinomas (Grade 1) indicated lower S-phase values as compared to the undifferentiated (Grade 3) ones. S-phase values estimated by FCM were about two times higher than the 3H-thymidine labeling index (LI) obtained by an in vitro procedure. The data estimated in this study showed that DNA determinations as an adjunct to conventional histopathologic assessment may provide objective clinically relevant information with respect to the degree of malignancy and prognosis of patients with breast carcinoma.     

软组织肿瘤的病理分级,DNA含量测定及图像分析

Flow cytometry and image analysis technique were used to quantitate the nuclei of various soft tissue tumors. A single representing section from soft tissue sarcoma was used for histologic grading. Histologic and cytometric comparative analyses showed that all 21 benign tumors were diploid. Among 62 cases of soft tissue sarcoma, 45 (73%) were aneuploid. There was a significant difference in the nuclear area between benign and malignant tumors (P less than 0.01), diploid and aneuploid tumors (P less than 0.05). The two new techniques are valuable in cellular quantitative measurement for soft tissue tumors.     

Correlation of model chromosome number of cultured non-small cell lung carcinomas with DNA index of solid tumor tissue.

The modal chromosome number of 13 non-small cell lung carcinomas placed into culture was compared to the DNA index of the tumor tissue as measured by flow cytometry in order to determine whether cytogenetic results from such cultures are representative of the original solid tumor. The modal chromosome number observed in culture, which ranged from 45-146, fell within the range of aneuploidy predicted from the DNA content of the original tissue in all 13 cases. In 7 cases, flow cytometry results showed that the aneuploid G1/G0 population of the tumor tissue (DNA index of 1.5 or higher) represented 11-76% of the cells present, while diploid cells (presumably normal tissue) made up the remainder of the population. In these 7 cases, modal chromosome numbers of 61-92 were found in tumor cells cultured from the tissue. In 3 cases, only a diploid or near-diploid population was found by flow cytometry, consistent with the near-diploid modal chromosome number of cultured cells observed (45-55). In 3 cases, the aneuploid G1/G0 population (DNA index of 1.5, 1.6, and 3.2) of the original tissue represented only a small fraction of the solid tumor (1-5% of cells). Modal chromosome number found in cells cultured from these 3 cases was 64-69, 62-68, and 136-146, which is in close agreement with the aneuploid peak observed in the tissue. Histological analysis of the tumor tissue in two of the latter cases showed large numbers of infiltrating lymphocytes and/or stromal tissue which could have dominated the measurement by flow cytometry. In the third case, tumor cells made up at least 75% of the specimen examined, implying that part of the population in the "diploid" peak contained tumor cells in this specimen. Only the aneuploid population was detected in culture of this tumor. Agreement between flow cytometry and cytogenetics was found in cases in which metaphase spreads were obtained within a few days of culture as well as after several months. These results indicate that highly aneuploid populations are found in many, but not all, non-small cell lung tumors. Although in some cases multiple populations may exist in the tumor which do not all proliferate in vitro, tumor cells which are found in culture of solid lung carcinomas are representative of the original tumor. Flow cytometry findings in the solid tumors confirmed the findings of aneuploidy observed by cytogenetic analysis.     

Flow cytometric analysis of DNA in bone and soft-tissue tumors using nuclear suspensions

Ninety-four bone and soft tissue tumors were analyzed for their DNA content using flow cytometry (FCM). A simple, rapid method for preparing isolated nuclear suspensions was used. Tissues, minced in a hypotonic solution containing detergent and propidium iodide as a fluorescent probe for DNA, provided in most instances high nuclear yields from only 0.02 to 0.03 g of solid tumor. Whereas all nonneoplastic samples had a diploid DNA content, various degrees of abnormal DNA distributions were detected in 90% of the neoplastic samples and were present in benign as well as malignant tumors. Our findings demonstrate that FCM DNA analysis is practical in most musculoskeletal tumors and support the observations of others that abnormal DNA content may serve as a general neoplastic marker in these tumors.     

Predicting metastasis of pheochromocytomas using DNA flow cytometry and immunohistochemical markers of cell proliferation: A positive correlation between MIB-1 staining and malignant tumor behavior.

BACKGROUND: In the absence of metastases, there are no reliable microscopic features that distinguish malignant from benign pheochromocytomas. Because a common feature of malignancy is the loss of cell cycle regulation and normal growth arrest, the authors hypothesized that analysis of the cell cycle could be used to aid in the diagnosis of malignant pheochromocytoma. METHODS: Cell cycle analysis of archival samples of 51 pheochromocytomas (40 sporadic, 11 familial) from 45 patients, including 6 malignant and 45 benign tumors, was conducted. Flow cytometry data and immunohistochemistry for markers of cell proliferation (proliferating cell nuclear antigen [PCNA] and MIB-1 [Ki-67]) were correlated with the authors' clinical data base records, with a mean follow-up of 66 months. RESULTS: No correlation of DNA ploidy, S-phase fraction by flow cytometry, or PCNA with malignancy was observed. Staining for the MIB-1 nuclear proliferation marker was positive in 3 of 6 (50%) of the malignant pheochromocytomas and negative in all 45 benign tumors (P< 0.01). CONCLUSIONS: Contrary to some previous reports, a diploid DNA pattern does not necessarily predict benign behavior of pheochromocytoma. In this study, cell cycle analysis and, in particular, assessment of the MIB-1 nuclear proliferation marker was useful in the histologic evaluation of pheochromocytoma, as MIB-1 was expressed only in malignant tumors.     

DNA contents in Wilms' tumors. A cytofluorometric study

Cytofluorometric measurement of nuclear DNA was performed on individual tumor cells isolated from paraffin sections of Wilms' tumors. The DNA distribution of one untreated primary tumor showed the first major peak near the diploid range and the second peak in the tetraploid range. There were many cells having amounts of DNA interspersed between the diploid and tetraploid range. Polyploid cells were not observed. Most of the Wilms' tumor cells had a higher diploid DNA value than the small lymphocytes of the control cells. The primary tumor and its metastases showed similar DNA distribution patterns. After treatment, the distribution pattern showed a reduction in number of cells between the diploid and tetraploid range and in the tetraploid range, with the greater number of cells being found in the diploid range. Though the phases of the cell cycle are not always clearly detectable by cytofluorometry, the cells of the untreated Wilms' tumor were distributed into the phases of the cell cycle as follows: 65.9% in G0 and G1 phases; 31.2% in S-phase; and 2.9% in G2 and M phases.     

Evaluation of DNA ploidy and degree of DNA abnormality in benign and malignant melanocytic lesions of the skin using video imaging

BACKGROUND: Making a morphologic distinction between benign and malignant melanocytic tumors of the skin is frequently difficult, especially because "gray zones" between these lesions often exist. DNA image cytometry as an adjuvant method for the diagnosis and prognostic prediction of premalignant lesions and malignant tumors of many other organs is already well established. The aim of this study was to determine whether DNA image cytometry is helpful in distinguishing benign from malignant melanocytic lesions and whether cytometry would give valid information with which to predict the prognoses associated with malignant melanomas. METHODS: DNA image cytometry was performed on 127 benign and 58 primary maligant melanomas of the skin as well as 11 metastatic melanomas, using an enzymatic single cell solution according to a method described by Heiden et al. in Cytometry (1991;12:614-21). RESULTS: DNA aneuploidy was graded by DNA index (DI) and a 2c deviation index (2cDI). In contrast to benign melanocytic lesions (with 16% DNA aneuploidy), primary and metastatic malignant melanomas had significantly higher frequencies of DNA aneuploidy (86% and 73%, respectively). In the degree of DNA aneuploidy, significant differences between benign and malignant melanocytic tumors could be observed. The mean 2cDI of aneuploid benign lesions was 1.0, whereas the primary malignant melanomas had a mean 2cDI of 2.92 and the metastatic melanomas a mean of 6.9. The frequency of DNA aneuploidy increased with Breslow thickness. Twenty-one patients with primary malignant melanoma developed metastases. All metastasizing primary tumors were aneuploid and showed a significantly higher grade of DNA aneuploidy than nonmetastasizing malignant melanomas. Moreover, none of the diploid malignant melanomas developed metastases. CONCLUSIONS: This study reveals that DNA image cytometry is prognostically and diagnostically relevant to the evaluation of melanocytic lesions of the skin. Nevertheless, it cannot be relied on alone to provide enough information for a diagnosis.     

Detection of p53 Gene Mutations in Aspiration Biopsy Specimens from Suspected Breast Cancers by Polymerase Chain Reaction-Single Strand Conformation Polymorphism Analysis

Genomic DNA was extracted from aspiration biopsy specimens taken from 15 suspected cases of breast cancer, including 7 known cases of breast cancer, and the p53 gene was studied for evidence of mutation by using a polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) analysis. In 5 of the 15'cases (33%), p53 gene mutation was identified and these tumors were subsequently histologically diagnosed as malignant. Further, DNA flow cytometry of the 15 tumors demonstrated that 6 (40%) were aneuploid and malignant, whereas 9 (60%) were diploid and benign. It was also found that the tumor cells in 5 aspirated cases that showed p53 gene mutations were all aneuploid, the p53 protein expression was positive, and the tumors were proved to be histologically malignant. It was thus concluded that the detection of p53 gene mutation by PCR-SSCP analysis of aspirated biopsy specimens from suspected breast cancers is a helpful method for achieving a more accurate diagnosis.     

Flow cytometric analysis of nuclear DNA content in ovarian tumors. Association of ploidy with tumor type, histologic grade, and clinical stage.

The authors undertook a prospective, flow cytometric study of nuclear DNA ploidy in 140 fresh ovarian tumors. There were 43 benign tumors, 27 borderline tumors, and 70 malignant tumors. Results of DNA ploidy analysis were compared to age at diagnosis, menopausal status, tumor size, histologic type, grade, and International Federation of Gynecology and Obstetrics (FIGO) stage. Although the majority of benign tumors were diploid, 19% were aneuploid. Among the benign tumors, DNA ploidy was significantly associated with tumor type and tumor size. All borderline tumors were diploid. Of the 70 malignant tumors, 64% were aneuploid. In the malignant tumors, DNA aneuploidy had significant univariate associations with histologic type, grade, and FIGO stage. By multivariate analysis, DNA aneuploidy remained significantly associated with stage and grade, both known predictors of survival in ovarian cancer. These results indicate that DNA ploidy varies with the aggressive potential of an ovarian cancer and may, at the time of initial diagnosis, provide additional information about tumor prognosis.     

Statin immunolocalization in human brain tumors. Detection of noncycling cells using a novel marker of cell quiescence.

Surgical specimens of 35 human brain tumors were examined with a novel monoclonal antibody, S-44, immunoreactive to statin, a nuclear protein specifically expressed in quiescent (noncycling) G0-phase cells. Benign tumors typically were statin positive with labeling indices (LI) between 22% and 96%: acoustic schwannomas (n = 3, mean = 29.9 +/- 19.4%); meningiomas (n = 4, mean = 59.0 +/- 15.1%); pituitary adenomas (n = 3, mean = 79.9 +/- 28.2%), and an epidermoid cyst (41.0%). By contrast, the statin LI of 18 of 24 (75%) malignant brain tumors was less than or equal to 2%: medulloblastomas (n = 7, mean = 0.3 +/- 0.2%); anaplastic astrocytomas (n = 3, mean = 1.6 +/- 2.7%); glioblastomas (n = 10, mean = 10.3 +/- 14.4%); metastatic carcinomas (n = 3, mean = 3.0 +/- 4.6); and a germinoma (0.2%). The vascular endothelium among diverse tumors typically was statin positive. All 21 tumors with a statin LI less than 10% were malignant, and all nine tumors with a statin LI greater than 40% were benign. The statin LI of benign tumors (n = 11, mean = 55.1 +/- 26.7%) was significantly higher than that of the malignant tumors (n = 24, mean = 5.2 +/- 10.5%, P less than 0.001). The absence of statin expression is a new way to determine the malignancy of human brain tumors. The statin LI may be useful to guide the prognosis and treatment of individual patients. The mechanisms that control statin expression are important in therapy seeking to shift the proliferating, cycling cells to the quiescent, G0 compartment.     

The clinical relevance of ploidy and S-phase fraction determination in salivary gland tumors: a flow cytometric study of 97 cases

BACKGROUND: The authors studied a series of 97 consecutive cases of salivary gland tumors to investigate the correlation between the biologic parameters DNA ploidy and S-phase fraction (SPF) and the presumptive behavior of the neoplasms, as well as their potential clinical utility. METHODS: Histopathologic classification and grading of the tumors were evaluated according to 1991 World Health Organization criteria. DNA analysis was performed by flow cytometry in fresh material after propidium iodide staining. Clinical data and follow-up information were obtained from the clinical charts. RESULTS: All the 71 benign salivary tumors showed a DNA diploid pattern. Seven carcinomas (7.2%) exhibited DNA aneuploidy. Eleven (42.3%) of 26 malignant tumors were considered low grade carcinomas, all of them being DNA diploid. Of the remaining 15 tumors, classified as high grade carcinomas, 7 showed DNA aneuploidy. SPF values ranged from 0.6% to 27.7%. A statistically significant difference was found between the mean SPF values of benign and malignant tumors, diploid and aneuploid tumors, and low grade and high grade carcinomas. When a cutoff value of 3% was used to discriminate histopathologic subgroups with prognostic impact, a significant difference was found between benign and malignant salivary tumors, high grade and low grade carcinomas, and high grade and benign tumors (P < 0.001). CONCLUSIONS: The data from this study confirm the low incidence of DNA aneuploidy in salivary gland tumors and suggest the potential utility of SPF estimation in evaluating the clinical behavior of these neoplasms.     

HISTOLOGIC GRADE, AND CONTENT AND IMAGE ANALYSIS OF SOFT TISSUE TUMORS

Flow cytometry and image analysis technique were used to quantltate the nuclei of various soft tissue tumors. A single representing section from soft tissue sarcoma was used for histologic grading. Histologlc and cytometric comparative analyses showed that all 21 benign tumors were diploid. Among 62 cases of soft tissue sarcoma, 45(73%) were aneuploid. There was a significant difference in the nuclear area between benign and malignant tumors (P<0. 01), dlploid and aneuploid tumors (P<0. 05). The two new techniques are valuable In cellular quantitative measurement for soft tissue tumors.     

The significance of bivariate cytokeratin and DNA flow cytometry in paraffin-embedded specimens of non-small cell lung cancer

Background. The presence of non-tumor cells inside cancer tissue is one of the causes of errors in cell cycle analysis by DNA flow cytometry. The recent establishment of bivariate cytokeratin and DNA flow cytometry has made feasible the accurate assessment of tumor proliferative activity. Methods. Bivariate flow cytometry and immunohistochemistry examinations of paraffin-embedded specimens were performed in 92 patients with non-small cell lung cancer (NSCLC). Determination of the S-phase fraction by flow cytometry, with cytokeratin gating (CK-gated SPF) and without gating (ungated SPF), and the expression of proliferating cell nuclear antigen by immunohistochemistry (PCNA labeling index), were used to assess cancer cell proliferation. Results. Two tumors had DNA histograms with a coefficient of variation of more than 8.0% and were excluded from the flow cytometric analysis. In DNA diploid tumors (n = 25), the ungated SPFs (8.7 ± 3.6%) showed a lower distribution than the CK-gated SPFs (14.3 ± 4.7%) (P < 0.0001). In DNA aneuploid tumors (n = 65), there was no difference in distribution between the ungated SPFs (15.0 ± 8.3%) and the CK-gated SPFs (15.1 ± 7.1%) (P = 0.94). The CK-gated SPF and the PCNA labeling index of an individual tumor had a good correlation (P < 0.0001), and this agreed with the result showing that DNA diploid and aneuploid tumors had equal proliferative activity (P = 0.64 and P = 0.63, respectively). Conclusion. The technique using CK-gating markedly improved the SPF measurement in DNA diploid tumors. This assessment showed no difference in proliferative activity between DNA diploid and aneuploid tumors in NSCLC. Bivariate cytokeratin and DNA flow cytometry is an accurate and objective method for cancer-specific analysis, and will surely be informative in clinical oncology. Received: February 22, 2001 / Accepted: June 28, 2001