PROGNOSTIC IMPORTANCE OF THYMIDYLATE SYNTHASE EXPRESSION IN EARLY BREAST-CANCER

Purpose: To assess the prognostic importance of thymidylate synthase ( TS) expression in breast tumors of patients with early-stage breast ca ncer, and to determine whether the benefit of chemotherapy (CT) is ass ociated with TS expression. Patients and Methods: The level of TS expr ession was evaluated in 210 negative and 278 node-positive patients en rolled onto Trial V of the international Breast Cancer Study Group ([I BCSG] formerly the Ludwig Breast Cancer Study Group) with a median fol low-up time of 8.5 years. TS expression was assessed using the immunoh istochemical method with the monoclonal antibody TS 106 on paraffin-em bedded tissue specimens. Results: High TS expression was associated wi th a significantly worse prognosis in node-positive but not in node-ne gative breast cancer patients. Twenty-seven percent of node-positive p atients with high TS expression were disease-free at 10 years, compare d with 44% of node-positive patients with low TS expression (P=.03). F orty-one percent of patients with node-positive high-TS-expressing tum ors were alive after 10 years, compared with 49% of those with low TS expression (P=.06). The association between TS and disease-free surviv al (DFS) and overall survival (OS) wets independent of other prognosti c factors such as tumor size, tumor grade, nodal status, vessel invasi on, estrogen receptor (ER)/progestin receptor (PR) status, c-erb 8-2, or Ki-67 expression. In node-positive patients, six cycles of standard adjuvant cyclophosphamide, methotrexate, and fluorouracil ([5-FU] CMF ) CT improved DFS and OS compared with one cycle of perioperative CMF therapy. The magnitude of this benefit was greatest in patients whose tumors had high TS expression (P <.01 for DFS; P <.01 for OS). Node-ne gative patients demonstrated no difference in outcome to CT based on T S expression; however, the power to detect differences was limited by the small number of events in this group. Conclusion: In early-stage b reast cancer, high TS expression is associated with a significantly wo rse prognosis in node-positive patients. Node-positive patients with h igh TS levels demonstrate the most significant improvement in DFS and OS when treated with six cycles of conventional adjuvant CMF therapy.