A new measurement of residual cancer burden to predict survival after neoadjuvant chemotherapy

Abstract

536 Background: The strength of association between tumor response and survival is critical for neoadjuvant chemotherapy trials. Pathologic complete response (pCR) reliably predicts survival benefit, but residual disease contains a range of pathologic responses that likely contain different prognostic groups, including near complete response and resistance. Methods: Pathologic slides and reports were reviewed from 432 patients in two completed neoadjuvant trials: 1) fluorouracil, doxorubicin and cyclophosphamide (FAC) in 189 patients, and 2) paclitaxel followed by FAC (T/FAC) in 243 patients. Paclitaxel was administered as twelve weekly (n=126) or four 3-weekly cycles (n=117). Residual cancer burden (RCB) was calculated as an index that combines pathologic measurements of primary tumor (size and cellularity) and nodal metastases (number and size). We compared four RCB categories, from RCB-0 (pCR) to RCB-3 (chemoresistant), and post-treatment revised AJCC Stage (0-III) for prediction of distant relapse-free survival (DRFS) in multivariate Cox regression analyses (stratified by ER status). Results: The pCR rate was greater after T/FAC than FAC (24% vs. 16%, LR p<0.05), and after weekly (vs. 3-weekly) paclitaxel in T/FAC (30% vs. 16%, LR p<0.01). In patients with residual disease, RCB measurements were significantly lower after T/FAC than FAC (t-test, p<0.0001), but were not different between paclitaxel schedules in T/FAC. RCB was a continuous predictor of DRFS after T/FAC (HR=1.86, 95%CI 1.51–2.30) or FAC (HR=1.67, CI 1.38–2.01) with median follow-up 5 and 8 years, respectively. The resistant category RCB-3 predicted relapse more strongly than AJCC Stage III and identified a larger group of high-risk patients ( Table ). Conclusions: RCB is a new continuous measure of pathologic response that is defined from routine pathologic materials, represents the distribution of residual disease, is a significant predictor of DRFS, and defines chemotherapy resistance more effectively than revised AJCC Stage. [Table: see text] [Table: see text]