DNA analysis and S-phase fraction determination by flow cytometric analysis of infiltrating lobular carcinoma of the breast.

Flow cytometric analysis was performed on 50 infiltrating labular carcinomas (ILCs) of the breast from 50 patients with clinical follow-up (average duration, 4.1 yr) who had been treated between 1976 and 1991. The patients were classified as alive with no evidence of disease, alive with disease, or dead of disease. Ploidy and S-phase fraction (SPF) were compared with clinical outcome, histologic pattern (classical versus variant patterns), nuclear grade 1 or 2, axillary lymph node status, tumor size, percentage of signet ring cells, and estrogen receptor status. There was no association between aneuploid or diploid ILC and disease recurrence (of those patients classified as alive with no evidence of disease plus dead of disease, 4 (40%) of 10 were aneuploid and 15 (38%) of 40 were diploid), survival (of those classified as alive with no evidence of disease plus alive with disease, 9 (90%) of 10 were aneuploid and 36 (90%) of 40 were diploid), or any of the other factors evaluated. However, ILCs with a high SPF were more likely to recur than those with a low SPF (a high SPF was found in 9 [56%] of 16; a low SPF was found in 9 [30%] of 30), but this relationship was not statistically significant (P = 0.08). When only diploid ILCs were considered, there was a statistically significant association between high SPF and recurrence (a high SPF was found in 9 [64%] of 14, a low SPF was found in 6 [24%] of 25, P = 0.033). After the stratification of the diploid ILCs by the stage of disease, this relationship persisted only in Stage 1 (recurrence: a high SPF was found in 3 [75%] of 4; a low SPF was found in 1 [9%] of 11, P = 0.033). There was no association between SPF and any of the other factors evaluated. Our study indicates that ILC is usually diploid and that SPF may be a prognostic indicator that is limited to Stage 1 disease.