In vitro thymidine labelling index in primary operable breast cancer.

The in vitro Thymidine Labelling Index (TLI) of 164 primary breast carcinoma was measured. The relationship of TLI to other established prognostic variables was examined, and the rates of of recurrence and survival of groups of women with high and low TLI tumours were compared. Poorly differentiated tumours had significantly greater TLI values but there were no significant associations with tumour size, axillary lymph node status, age and menopausal status or steroid receptor status. Although there were more recurrences and deaths in the group of women with high TLI tumours, these differences were not statistically significant. In vitro TLI may be a further expression of tumour differentiation, rather than cellular proliferation, and from this study does not provide any additional prognostic information.