Interaction of tamoxifen with concurrent cytotoxic adjuvant treatment affects lymphocytes and lymphocyte subsets counts in breast cancer patients.

The effects and interaction of endocrine and cytotoxic adjuvant treatment on measures of cellular immunity were assessed in 41 stage I-II breast cancer patients from International Breast Cancer Study Group trials. Counts of lymphocytes and lymphocyte subsets [(T, T4, T8, B, natural killer (NK) and activated T (AT) cells] were assessed by flow cytometry immediately before adjuvant therapy at baseline and on day 1 of the 3rd cycle. Twenty-two patients received cyclophosphamide, methotrexate and 5-fluorouracil (CMF), 7 CMF and tamoxifen (TAM), and 12 TAM alone. On day 1 of the 3rd cycle the counts of total lymphocytes (P = 0.003) and all lymphocyte subsets (P<0.05) except AT cells were significantly lower than baseline in the CMF treatment group. There was no significant change in the CMF+TAM or in the TAM treatment group. The combination of CMF and TAM resulted in less pronounced decrease in lymphocyte and subset counts from baseline to day 1 of the 3rd cycle. It seems possible that there is an interaction between TAM with CMF that affects lymphocyte and lymphocyte subset counts during cytotoxic treatment.