HER2 status on persistent disseminated tumor cells after adjuvant therapy may differ from initial HER2 status on primary tumor.

BACKGROUND: Persistence of disseminated tumor cells (DTCs) is observed in 10 to 15% of breast cancer patients and is associated with poor prognosis. These patients might benefit from secondary adjuvant targeted therapy. The aim of this study was to assess HER2 status of persistent DTCs to determine whether the use of HER2-targeted agents might be a therapeutic option in patients with tumor cell persistence. PATIENTS AND METHODS: Bone marrow was obtained from 85 primary breast cancer patients intraoperatively and after completion of systemic treatment (median follow-up of 13 months; range: 6-30 months). Immunofluorescence double staining was used for identification of cytokeratin-positive, HER2-positive cells.
RESULTS: A total of 31 out of 85 (36%) patients had DTCs preoperatively. Out of 85 (16%) patients, 14 were DTC positive after completion of surgery and adjuvant cytotoxic therapy. Five of these patients had HER2-positive DTCs, however, the corresponding tumor was HER2 positive in only one case. The remaining nine patients with HER2-negative DTCs had HER2-negative primary tumors.
CONCLUSION: HER2-positive DTCs can be detected in patients with HER2-negative tumors, even after adjuvant therapy. Such patients may benefit from (secondary) HER2-targeted therapy in an adjuvant setting.