Abstract ES9-3: ES9-3 (Neo)adjuvant systemic therapy of TNBC: How much is enough?

The use of neoadjuvant chemotherapy in ER-negative cancers has become quite popular in patients with stage II and III breast cancers, since it gives us important information on long-term prognosis, based on the amount of residual disease burden at the time of definitive surgical resection. Two relatively large phase II randomized neoadjuvant clinical trials have explored the addition of carboplatin to an anthracycline/taxane based chemotherapy regimen for patients with stage II or III triple-negative breast cancers (TNBC): GeparSixto, in Europe, and CALGB40603, in the US. Despite significant differences in chemotherapy backbone, and frequency and duration of carbo administration, both trials showed that the addition of carboplatin significantly increased the rate of pCR from ∼ 40% to 54%. Both trials also reported a significant amount of added toxicity for the carboplatin arms, with a significant amount of patient not being able to complete their planned treatment. However, whereas the GeparSixto trial reported an improvement in 3-year disease-free survival (DFS), the CALGB40603 did not. Since neither of these studies was powered to address disease-free or overall survival benefit from the addition of carboplatin to neoadjuvant systemic chemotherapy, lack of precision from small sample sizes are likely responsible for the difference seen in DFS between these two trials. Additionally, there9s not yet a confirmed correlation between increases in frequency of pCR and event-free survival (EFS). A recently pooled analysis by Cortazar et al. could not validate pCR as a surrogate endpoint for improved EFS and overall survival (OS): as some patients who achieve a pCR go on to relapse and many with residual disease never experience a recurrence, small differences in pCR may never translate to improvements in EFS. Long term effects of the added toxicity of carboplatin are also not known. At present, upon completion of neoadjuvant therapy, the standard of care for patients with TNBC (who have no clinical evidence of metastatic disease after surgical excision of the cancer regardless of burden of residual disease) is observation. But recently, preliminary data from a Japanese phase III trial (CREATE-X) that randomized patients with HER2-negative breast cancer with lack of pCR post-neoadjuvant chemotherapy to observation or capecitabine x 8 cycles showed that the addition of capecitabine provided a statistically significantly higher 5-year DFS and OS in the TNBC group. EA1131, an ongoing adjuvant randomized phase III clinical trial seeks to address if patients with basal-like TNBC, with high risk of recurrence due to residual disease post completion of neoadjuvant chemotherapy, have a higher DFS benefit from a platinum agent than from capecitabine. The results of this trial will ultimately help avoid exposing upfront unselected patients, many of whom will never relapse, to toxic therapy in the absence of long-term known benefit. In summary, the addition of a platinum agent routinely in the neoadjuvant setting in TNBC is still an individualized decision and not yet standard of care for all patients. The decision to use capecitabine in patients with residual disease post-neoadjuvant chemo may still be slightly premature, confirmatory results of EA1131 are eagerly awaited. Citation Format: Mayer IA. ES9-3 (Neo)adjuvant systemic therapy of TNBC: How much is enough? [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr ES9-3.