Dilution effect of nontumor cells on flow cytometric DNA S-phase fraction in breast cancer fine needle aspirates

OBJECTIVE: To analyze the proportion of nontumor cells in fine needle aspirates of breast carcinoma and its influence on flow cytometric S-phase fraction (SPF) estimation. STUDY DESIGN: We analyzed the proportion of nontumor cells in fine needle aspiration biopsy smears, performed flow cytometric analysis of DNA ploidy and SPF on freshly aspirated tumor material and analyzed histograms manually and automatically using Multi-Cycle AV software (Phoenix Flow Systems, San Diego, California, U.S.A.) for cell cycle analysis. We corrected SPF of diploid tumors for the dilution effect using an individually established percentage of nontumor cells (individual correction) and the mean proportion of nontumor cells in diploid tumors (factor correction). RESULTS: The proportion of nontumor cells ranged from 0.5% to 76.6% (mean, 12.6; SD, 15.7) in 55 diploid tumors and from 0.5% to 53% (mean, 8.6; SD, 8.9) in 84 aneuploid tumors (p=0.178). In 14 of 139 (10%) samples, the proportion of nontumor cells exceeded 20%. The mean SPF values of diploid tumors without correction were 4.9% (manually) and 6.5% (automatically) and of aneuploid tumors, 9.5% and 11.0%, respectively. In univariate Cox survival analysis, noncorrected SPF was a significant prognostic factor in overall survival (p < 0.001). Neither individual nor factor correction of SPF significantly changed its prognostic value. CONCLUSION: Fine needle aspirates contain low proportions of nontumor cells, having an insignificant dilution effect on SPF estimation. Most probably, SPF could be reliably estimated usingfreshly aspirated tumor material without any correction or adjustment.