The idea of thymidine phosphorylase upregulation by the combination of capecitabine and docetaxel upon which this study was largely based34–36 has since been disputed.47 The primary endpoint of this trial of a novel platinum- based regimen was a pCR rate of 15%. It is significant that 83% of the pCRs were in triple-negative tumors. A secondary endpoint of MRD was calculated, as this was in the original design of the study, but ultimately was not relevant to the primary endpoint.
Ultimately, pCR is the more relevant point of discussion for the modern era. The 15% pCR rate seen in this phase II study was within range of those achieved in numerous other phase II/III neoadjuvant chemotherapy trials with ≥ 25 patients, ≥ 3 cycles of chemotherapy, and pCR defined as absence of carcinoma in the breast and axilla. To date, no patient in our study with a pCR has been noted to have recurrent disease. However, a recently published French study found a 22% recurrence rate at 11 years in patients with triple-negative breast cancer achieving pCR, highlighting the importance of longer-term follow- up.48.
The inclusion of patients with HER2-positive disease in neoadjuvant studies without HER2-targeted therapy was standard at the time that this study was conducted, but is no longer appropriate. If we were to exclude the eight HER2-positive patients from analysis, then there would be only 34 patients evaluable for response, with a pCR rate of 18%. Buzdar et al33 demonstrated a 65% pCR rate in women with HER2-positive disease treated with neoadjuvant chemotherapy plus trastuzumab. The improvement in pCR with the addition of trastuzumab is supported by other confirmatory trials. Authors of a single-arm trial of dose-dense epirubicin and cyclophosphamide followed by dosedense docetaxel and trastuzumab in a HER2-positive population reported a pCR rate of 57%.49 The randomized NOAH study50 achieved a pCR rate of 23% in 115 patients treated with trastuzumab-based chemotherapy.
It is interesting to note that five of six patients (83%) achieving a pCR in our study had triple-negative tumors. Investigators at the University of Miami presented a retrospective review of locally advanced triple-negative breast cancer treated with docetaxel and a platinum salt, with 61% of patients also receiving AC. The authors reported a pCR rate of 34% overall and 40% for patients receiving AC.51 A pCR rate of 60% was noted in the triplenegative subset of patients in another study evaluating docetaxel, doxorubicin, and cyclophosphamide with or without vinorelbine/capecitabine (GeparTrio Study).52 Further, a pCR rate of 72% was achieved with singleagent cisplatin in a group of 25 women with BRCA1 mutations, suggesting, if confirmed by others, that this largely triple- negative population may be exquisitely sensitive to platinum salts.43 In contrast, in a previous study of cisplatin in BRCA mutation carriers, Garber et al44 reported a pCR rate of 22%, suggesting that further trials are needed specifically in BRCA carriers and in triple-negative tumors to see whether these specific patient subsets preferentially derive benefit from platinum salts in the neoadjuvant setting.
The results of the current study are consistent with others indicating a low likelihood of pCR in patients with ERpositive tumors. In fact, none of our ER-positive patients had a pCR. Neoadjuvant endocrine therapy in postmenopausal women with ER- and/ or PR-positive disease is a reasonable treatment option for selected patients, but endpoints other than pCR have often been used.53,54 It is therefore difficult to directly compare these two strategies. Currently, investigators are comparing the three aromatase inhibitors head to head in the neoadjuvant setting for postmenopausal women with hormone receptor–positive tumors.55
The historic pCR ceiling appears to be rising, albeit slowly. Where targets such as HER2 overexpression and triple- negative biology are recognized, progress is being made. Patient eligibility criteria for neoadjuvant breast cancer studies at the time of this trial were quite broad, and it is now recognized that specific subsets of breast cancer respond differently to different classes of agents. Furthermore, our knowledge about breast cancer prognostic markers continues to expand. Had this study been designed in 2011, other data points such as Ki67 would have been collected. A recently published study on neoadjuvant triplenegative breast cancer found that only patients with baseline Ki67% expression > 10% achieved pCR.56
Given the long-term implications of not achieving pCR, optimal treatment of patients in the adjuvant setting is critical. Although neoadjuvantly treated patients with ER-positive or HER2-positive disease go on to receive adjuvant agents (antihormonal therapy for ER-positive disease and trastuzumab for HER2-positive disease), patients with triple-negative disease lack long-term therapies of proven efficacy. Perhaps, as we edge closer to defining the optimal neoadjuvant agents for each subset of patients, this will be less of a concern. Many earlyphase neoadjuvant studies have been conducted, with promising reports, yet the results of larger, randomized trials continue to frustrate both investigators and clinicians. These deficits in care can only be answered by carefully planned randomized clinical trials.