CHICAGO – A circulating tumor cell (CTC) count less than 5 per 7.5 mL of blood in patients with metastatic breast cancer indicates an indolent disease subset, according to a pooled analysis of individual patient data from two large cohorts.
The findings, which were independent of molecular subtype, disease location, or line of treatment, have important implications for CTC-based staging of metastatic breast cancer (MBC), which in turn could guide treatment decision making and drug development, Andrew A. Davis, MD, of Northwestern University, Chicago, and his colleagues reported in a poster at the annual meeting of the American Society of Clinical Oncology.
In 1,944 patients from the European Pooled Analysis Consortium (EPAC) and 492 from MD Anderson Cancer Center, CTC counts of 5 per 7.5mL or greater were associated with worse outcomes overall (hazard ratio, 2.43), the investigators said.
Median overall survival (OS) among all patients with CTC counts less than 5, who were considered to have stage IV indolent disease (stage IVindolent), was 36.3 months, and OS among those with de novo disease and CDC counts less than 5 was greater than 5.5 years, they said, noting that the survival benefit persisted across all disease subtypes.
For example, median OS in patients with stage IVindolent vs. stage IVaggressive (those with CTC counts of 5 or greater ) was 44.0 vs. 17.3 months in patients with hormone receptor–positive disease, 23.8 vs. 9.0 months in triple negative breast cancer patients, and 36.7 vs. 20.4 months in patients with HER2+ disease, respectively, they explained.They also noted that stage IVindolent disease could discriminate a less aggressive cohort both for patients with and without prior treatment; the hazard ratios were 0.40 and 0.42 favoring indolent disease for both first-line treatment and treatment beyond the first line, respectively.
In early-stage breast cancer, diagnostic tools have been incorporated into practice to help identify patients who will benefit from conservative vs. aggressive therapy, and the current findings suggest that CTC counts could be used in that manner for staging MBC.
“We propose a CTC-based staging system for MBC based on indolent and aggressive disease to incorporate into the American Joint Committee on Cancer [tumor node metastasis] staging classification,” they wrote, adding that prospective studies of single-agent, cost-effective treatments for stage IVindolent disease in the first-line setting are needed.
This study was supported by the Lynn Sage Breast Cancer Research OncoSET Program at Robert H. Lurie Cancer Center. Dr. Davis reported having no disclosures.
SOURCE: Davis A et al., ASCO 2018 .