Impact of neoadjuvant chemotherapy in stage II-III triple negative breast cancer on eligibility for breast-conserving surgery and breast conservation rates: surgical results from CALGB 40603 (Alliance).

Objective: To assess the efficacy of neoadjuvant systemic therapy (NST) at increasing the rate of successful breast-conserving therapy (BCT) in triple negative breast cancer.
Background: Inducing tumor regression to permit BCT is often cited to support administration of NST. To quantify this benefit, we conducted a surgical companion study to CALGB40603, a randomized phase II, 2×2 factorial trial of neoadjuvant paclitaxel ± carboplatin ± bevacizumab (B) followed by doxorubicin plus cyclophosphamide ± B in stage II-III triple negative breast cancer.
Methods: Before and after NST, treating surgeons evaluated BCT candidacy by clinico-radiographic criteria; surgery performed was at surgeon and patient discretion. We measured (1) conversion rates from BCT-ineligible to BCT-eligible, (2) surgical choices in BCT candidates, and (3) rates of successful BCT with tumor-free margins.
Results: Four hundred four patients were assessable for surgical outcomes. Two hundred nineteen (54%) were BCT candidates before NST. One hundred ninety-seven (90%) remained BCT candidates after NST, of whom 138 (70%) chose BCT, which was successful in 130 (94%). Of 185 (46%) who were not BCT candidates before NST, 78 (42%) converted to candidates with NST. Of these, 53 (68%) chose BCT with a 91% (48/53) success rate. The overall BCT-eligibility rate rose from 54% to 68% (275/404) with NST. Addition of carboplatin, B, or both increased conversion rates.
Conclusions: This is the first study to document prospectively a 42% conversion rate from BCT-ineligible to BCT-eligible, resulting in a 14% absolute increase in BCT eligibility. BCT was successful in 93% of patients who opted for it, but 31% of BCT-eligible patients still chose mastectomy.