A proposed classification of breast cancer based on kinetic information derived from a comparison of risk factors in 168 primary operable breast cancers

Flow cytometric DNA analysis was performed on 168 consecutive primary operable breast cancers and the results correlated with thymidine labeling, estrogen receptor (ER) and progesterone receptor values, and various histologic parameters. Seventy‐five cancers (45.0%) were diploid and 93 (55.0%) aneuploid. In 83.9% of aneuploid cancers, the DNA index fell between 1.1 and 2.0. Thirteen cancers were hypertetraploid and three hypodiploid. The percent of S‐phase cancers (SpF) varied from 1.1% to 24.4%, with a mean of 8.0% and a median of 7.1%. The mean SpF of diploid cancers was 5.2%; of aneuploid cancers, 10.3%. There was no significant correlation between SpF or ploidy and tumor size or axillary lymph node status. The thymidine labeling index (TLI) varied from 0.2 to 23.1, with a mean of 7.5 and a median of 6.1. There was good correlation between TLI and SpF (r = 0.892, P = 0.0001). ER‐negative tumors had a significantly higher mean SpF (10.3%) than did ER‐positive tumors (6.7%), but there was no significant correlation between ploidy and receptor positivity or negativity. There was a good correlation between invasive tumor necrosis, poor cytologic differentiation, aneuploidy, and above‐median SpF. Only a fair correlation was observed between mitotic rate and SpF. A classification of invasive breast cancers based on ploidy and SpF is proposed.