Background: Although current guidelines still support 5 years of hormone blocking therapy after primary breast cancer due to earlier results showing no benefit of longer treatment, recent data have shown that longer treatment with tamoxifen can better reduce recurrence and death. However, side effects with this therapy can be considerable and compliance declines with time. We, here, report data on monitoring circulating epithelial tumor cells (CETC) beyond maintenance therapy showing that even if maintenance therapy with SERM or aromatase inhibitors had been effective in reducing tumor cells in blood, there can be a reincrease after the end of maintenance therapy and that this is highly correlated with relapse.

Materials and methods: 7.5ml of anti-coagulated blood was drawn before the start of chemotherapy, after each cycle and after the end of chemotherapy. Using a nondissipative approach with only red blood cell lysis the white blood cells including the tumor cells were stained with a fluorescent labelled anti-epithelial antibody, positive events counted using an automated image analysis microscope and calculated per volume blood.

Results: 96 patients with nonmetastatic breat cancer were observed beyond maintenance treatment with hormone blocking therapy. Results on CETC were evaluable from 35 patients even after completion of therapy. Increasing cell numbers after the end of therapy were able to predict relapsing from long term relapse free survivors (p = 0.0001).

Conclusion: In breast cancer, a debate has been reiinitated with respect to the length of maintenane treatment. Even if hormone blocking maintenance treament is capable of reducing or even eliminating tumor cells circulating in peripheral blood and this is related to improved relapse free survival there may remain tumor cells in the body capable of regrowing and leading to late relapse. Monitoring of CETC in peripheral blood even after completion of maintenace therapy can early predict imminent relapse and help to decide whether to reinitiate hormone blocking therapy.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P1-13-11.