Chemotherapy use and surgical treatment by receptor subtype in node-negative T1a and T1b female breast cancers, Iowa SEER Registry, 2010 to 2012.

BACKGROUND

Patients with small node-negative breast tumors who are younger or who have human epidermal growth factor receptor 2-positive (HER2(+)) or triple-negative breast cancer (TNBC) subtypes are at increased risk of recurrence. Concurrently, systemic treatment recommendations have evolved. Less is known about how frequently cytotoxic chemotherapy is given to these patients. Mastectomy rates have also increased. This study reports the recent incidence of T1a,bN0M0 breast cancer and the characteristics associated with chemotherapy delivery and the surgery selected.

PATIENTS AND METHODS

This retrospective cohort is composed of invasive female breast cancers diagnosed with American Joint Committee on Cancer (AJCC) stage T1a,bN0M0 during 2010 to 2012 from the Iowa Surveillance, Epidemiology, and End Results (SEER) Cancer Registry. Chemotherapy use and surgery were identified by the registry. Univariate and multivariate analyses were performed to determine patient differences across subtype and factors associated with treatment.

RESULTS

The study included 1687 patients. This represented 27.6% of all AJCC stages I(a-c) to III breast cancer in 2010 to 2012, up from 18% in 1990 (P < .0001). Of 1456 patients with known subtype, 8.8% and 6.4% had HER2(+) and TNBC disease, respectively. Chemotherapy was given to 7.5% of women with T1aN0M0 and 12.7% of T1bN0M0 tumors. The likelihood of systemic treatment was associated with breast cancer subtype, tumor differentiation, and age in a multivariate model. The mastectomy rate was 31.8%.

CONCLUSION

Small node-negative breast cancers continue to grow significantly as a percentage of invasive breast cancer diagnoses. In 2010 to 2012 in Iowa, systemic chemotherapy correlated with risk factors associated with recurrence: age, subtype, and tumor differentiation. Relatively high rates of mastectomy were seen.