Circulating tumor cells in lobular versus ductal metastatic breast cancer

PURPOSE: Infiltrating lobular carcinoma (ILC) accounts for ~ 10% of all invasive breast cancer histologies. ILC is associated with worse prognosis than infiltrating ductal cancer. Circulating tumor cells (CTCs) are commonly elevated in metastatic breast cancer (mBC) and elevated levels of CTCs are associated with worse prognosis in breast cancers. We investigated CTC incidence in ILC in two patient cohorts. METHODS: . Findings were validated in a separate cohort of mBC patients who participated in a research protocol where CTC were analyzed. RESULTS: Within the EMERSE cohort of 218, 38 (17%), 29 (13%) and 151 (69%) patients, had lobular, mixed, and ductal mBC subtype, respectively. Overall, 101/218 (46%) patients had elevated CTC (≥ 5/7.5 ml whole blood). In this cohort, patients with ILC were more likely to have elevated CTCs (28/38; 74%) compared to those with mixed (14/29; 48%) or ductal (59/151; 39%) mBC (p = 0.001). In multivariate regression, patients with ILC were seven times more likely than ductal mBC to have elevated CTCs. These data were validated in 146 separate mBC patients in the research cohort. Elevated CTCs were detected in 79%, 31%, and 36% of patients with lobular, mixed and ductal mBC, respectively. CONCLUSION: CTC are more commonly elevated and tend to be higher in magnitude in patients with lobular compared to ductal mBC. CTC levels in mixed ductal-lobular morphology numerically more resemble ductal mBC.