Response rates and pathologic complete response by breast cancer molecular subtype following neoadjuvant chemotherapy

This is the largest study to date evaluating response rates and pathologic complete response (pCR) and predictors thereof, based on molecular subtype, in women with breast cancer having undergone neoadjuvant chemotherapy (NC).

The National Cancer Database was queried for women with cT1-4N1-3M0 breast cancer having received NC. Patients were divided into four subtypes: luminal A, luminal B, Her2, or triple negative (TN). Multivariable logistic regression ascertained factors associated with developing pCR. Kaplan-Meier analysis evaluated overall survival (OS) between patients by degree of response to NC when stratifying patients by subtype.

Of a total of 13,939 women, 322 (2%) were luminal A, 5941 (43%) luminal B, 2274 (16%) Her2, and 5402 (39%) TN. Overall, 19% of all patients achieved pCR, the lowest in luminal A (0.3%) and the highest in Her2 (38.7%). Molecular subtype was an independent predictor of both pCR and OS in this population. Clinical downstaging was associated with improved survival, mostly in women with luminal B, Her2, and TN subtypes. Subgroup analysis of the pCR population demonstrated 5-year OS in the luminal B, Her2, and TN cohorts of 93.0, 94.2, and 90.6%, respectively (Her2 vs. TN, p = 0.016).

Assessing nearly 14,000 women from a contemporary United States database, this is the largest known study examining the relationship between response to NC and molecular subtype. Women with luminal A disease are the least likely to undergo pCR, with the highest rates in Her2 disease. Degree of response is associated with OS, especially in luminal B, Her2, and TN patients. Despite the comparatively higher likelihood of achieving pCR in TN cases, this subgroup may still experience a survival detriment, which has implications for an ongoing national randomized trial.