Improved prognostic impact of S‐phase values from paraffin‐embedded breast and prostate carcinomas after correcting for nuclear slicing

Nuclear debris may significantly interfere with the analysis of S‐phase fraction (SPF) from paraffin‐embedded tumors. We used a background subtraction algorithm to compensate for the effects of slicing of tumor cell nuclei during preparation of paraffin‐embedded specimens. DNA histograms were analyzed from 88 node‐negative breast and from 78 prostatic carcinomas. Median SPFs corrected for nuclear slicing were lower than un‐corrected ones in both breast cancer (7.6% vs. 5.7%) and prostate cancer (6.7% vs. 4.2%). The median SPF value in each group was used as a cut‐off point in survival studies. As compared with the uncorrected SPFs, corrected SPF levels resulted in a more significant survival difference between breast cancer patients with above and below median SPF (p = 0.0014 vs. p = 0.014) and in a higher relative risk (RR) of death (4.5 vs. 3.1). The same was true for prostate cancer survival (p < 0.0001 vs. p = 0.002) and RR (5.3 vs. 3.1). Compared with the exponential background subtraction method, the sliced nuclei correction was more reproducible and could be applied in all evaluable histograms without the risk of overcompensation. In conclusion, our results support the use of background correction with the sliced nuclei model in DNA flow cytometric studies of archival tissues.