Platinum-based neoadjuvant chemotherapy in BRCA1-positive breast cancer: a retrospective cohort analysis and literature review

Hereditary breast cancer accounts for approximately 5–10% of all breast cancer cases. BRCA1/2 gene mutations are responsible for approximately two-thirds of hereditary breast cancers [1]. The BRCA genes are tumor suppressor genes that encode proteins that are involved in homologous recombination (HR) repair. HR is the most common repair mechanism for double strand breaks during the DNA replication process. Mutations in the BRCA gene result in genomic instability and subsequent malignant processes. The platinum agent introduces intra-strand crosslinks. Due to faulty DNA-repair proteins from the pathogenic BRCA1 mutation, cellular protein synthesis and replication are reduced, and eventually, cells undergo apoptosis. BRCA-associated breast cancers are often triple negative breast cancers (TNBCs). Due to significant differences in chemotherapy sensitivity that depend on hormone receptor status, various chemotherapy regimens have been tested in adjuvant and neoadjuvant settings for BRCA-associated breast cancer. Attempts to understand the role of BRCA genes in and sensitivity of cancer cells to DNA damaging agents in BRCA mutation carriers have reestablished interest in platinum agents in the context of breast cancer treatment.

Several studies have shown the sensitivity of BRCA-related breast cancer to platinum agents, such as cisplatin and carboplatin, and more studies will follow. The ESMO clinical practice guidelines [2] for primary breast cancer published in 2015 do not recommend platinum agents for routine use for BRCA1/2 mutation carriers; however, these guidelines state that adding a platinum compound to NACT, after discussion with the patient, is acceptable. The ESO-ESMO 3rd international consensus guidelines for advanced breast cancer (ABC3) [3] published on December 5th, 2016, recommend a platinum regimen chemotherapy for BRCA-associated TNBC if not previously administered.

The aim of this study was to retrospectively evaluate platinum-based neoadjuvant chemotherapy for BRCA1-positive breast cancers.

A retrospective evaluation was made of platinum-based neoadjuvant chemotherapy in breast cancer patients with BRCA1 gene mutations who were treated at the breast unit at Pauls Stradins Clinical University Hospital (PSCUH). Patient data were collected from the hospital database, along with the respective patient history and chemotherapy chart from the Clinic of Oncology at PSCUH. This retrospective evaluation was approved by Riga Stradins University Ethical committee (Nr.55/ 27.10.2016). Patients with diagnosed invasive breast cancers and confirmed BRCA1 gene mutations who received platinum-based chemotherapy in the neoadjuvant setting were included in the evaluation.

Insufficient patient data was the exclusion criterion. Pathological complete response was defined as the complete disappearance of an invasive tumor. The follow-up time was the time from mastectomy to February 2017.

Ten (83%) out of 12 patients achieved pCR after neoadjuvant chemotherapy. Two patients (17%) had residual cancer after NACT with partial response or stable disease. The proportions of the subgroups of those who achieved pCR are presented in Table 3. The pCR rates according to clinical stage I, II and III were 100%, 86% and 50%, respectively. Eight (80%) out of 10 patients with confirmed negative estrogen and progesterone receptor status achieved pCR. Five (83%) out of six patients with positive lymph node status prior to surgery achieved pCR. (Similarly, five (83%) out of six patients with node-negative disease achieved pCR).

Eleven patients are alive today, and one patient died due to brain metastases 15 months after breast cancer diagnosis. All 10 patients with pCR are disease free to date according to the available data. The mean observation time for the patient group with pCR is 25 months (range 6 – 63 months). Table 4 presents the characteristics of the two patients who did not achieve pCR.

Our findings from the retrospective evaluation at the breast unit of PSCUH suggested that platinum-based neoadjuvant chemotherapy was highly effective in breast cancer patients with BRCA1 gene mutations. In our patient group, 12 patients received platinum-based NACT. pCR was observed in10 patients (83%), and partial remission or stable disease was observed in two patients (17%). T. Byrski et al. [4] were the first to apply platinum-based chemotherapy in studies targeting BRCA mutation carriers specifically. As seen in Table 5, the pCR rates ranged from 59% to 83% in the evaluated studies. Our results matched these findings and confirmed the sensitivity of BRCA-associated breast cancer to platinum agents. In the neoadjuvant studies by T. Byrski [4, 5] and V. Moysienko [6], the authors applied cisplatin monotherapy. The patients in the current evaluation received cisplatin and doxorubicin (one patient received carboplatin and docetaxel). There were no available data on this combination for patients with BRCA-associated breast cancer. The results indicated that the addition of anthracycline to a platinum agent in the neoadjuvant setting produces equivalent or better results than monotherapy in terms of pCR. Most of the12 patients included in this evaluation had cancers that were diagnosed early. Seven patients had stage II, three patients had stage I, and two patients had stage III. These characteristics are comparable to the trial of T. Byrski et al. [5], where a pCR of 61% was achieved.

The BRCA1 founder mutations in our study included c.4035delA (BIC: 4154delA) and c.5266dupC (BIC: 5382insC). These are the same mutations examined in the study by Byrski et al.; however, C61G was also included in their study population but not in ours. Our results need to be verified in populations with other mutations.

Platinum agents also showed efficacy for BRCA1 mutation carriers with advanced breast cancer. A BRCA1 gene mutation was a good predictor of an increased response rate compared with wild-type BRCA1 [7‐9]. The best evidence on platinum efficacy compared to standard therapy to date is presented by Telli et al. in the TNT trial [7]. The authors randomized carboplatin vs docetaxel in patients with metastatic TNBC. They observed a carboplatin response rate of 68% vs a docetaxel rate of 33% (P = 0.03) in the subgroup of 43 patients having BRCA1/2 mutations. Further research is needed on metastatic BRCA-associated breast cancer.

There is a substantial amount of research on TNBC. In a study comprising 1824 patients with TNBC unselected for family history, 8.5% had a BRCA1 mutation, and 2.7% had a BRCA2 mutation [10]. The patients with BRCA-associated breast cancer represent a small subset of breast cancer patients. This is probably the reason for the lack of data for this specific patient population. To date, there are no available data from randomized trials that specifically target BRCA1 gene mutation carriers with breast cancer. Evidence from the Maksimenko study [11] indicated that carriers of a germline BRCA1 founder mutation (4153delA a 5382insC) had significantly improved prognoses at any stage compared to carriers of wild-type BRCA who had TNBC, even though only 7.8% of patients in this study had received platinum-based chemotherapy. These results may indicate that BRCA1 mutation carriers have higher chemosensitivity.

The toxicity of chemotherapy was not evaluated. Platinum agents are known to cause mild to severe toxicity [12]. Cisplatin seems to be the drug that has the most evidence of efficacy in BRCA-associated breast cancer. No evidence from randomized trials exists on which platinum agent is more effective in BRCA-associated breast cancer. Further data are needed. A transition from cisplatin to carboplatin-based chemotherapy would likely benefit patients in terms of fewer side effects and higher tolerance to recommended platinum dosages.

The results of the study confirm the high pCR rate of BRCA1-positive breast cancer after platinum-based neoadjuvant chemotherapy. Larger randomized studies and longer follow-up times are necessary to evaluate the role of platinum-based therapies in BRCA1-positive breast cancer.