Joyce A. O’Shaughnessy, MD
Although no cytotoxic agents are currently correlated with specific subtypes of triple negative breast cancer (TNBC), recent findings indicate that targeting genomic stability, antimetastatic mechanisms, and protein expression characteristics are promising approaches for future TNBC treatments.
Joyce A. O’Shaughnessy, MD, presented an overview of recent findings on chemotherapy regimens for TNBC at the 13th Annual International Congress on the Future of Breast Cancer, which Physicians’ Education Resource (PER) sponsored on July 17-19 in Huntington Beach, California.
According to O’Shaughnessy, therapy selection for TNBC is difficult because no subtyping approach has proved clinically useful thus far and most chemotherapeutic agents are nonselective.
However, genomic analyses of TNBC subtypes are yielding clues about potential ways to identify therapies. Notably, Vanderbilt-Ingram Cancer Center researchers have identified six subtypes of TNBC using gene expression profiling,1
and these insights help form the basis of emerging strategies, O’Shaughnessy indicated. She noted that research efforts are under way to identify assays and biomarkers to aid clinicians in matching therapies with patients.
Among unselected patients, single-agent studies indicate that a proportion of patients with TNBC respond extremely well to DNA-damaging platinum agents, such as cisplatin, doxorubicin, docetaxel, and epirubicin, in neoadjuvant therapy. Pathologic complete response (pCR) rates ranged from 9.6% among 73 patients treated with epirubicin to 27% among 28 patients who received docetaxel, said O’Shaughnessy.
The TBCRC 009 study showed that six patients who received cisplatin or carboplatin as a first-line treatment for metastatic TNBC were disease free without therapy for 22-53 months.2
Although the treatment was not randomized in this study, such a long disease-free period is extremely unusual in metastatic TNBC and the tumor characteristics of these high responders should be investigated further, according to O’Shaughnessy.
HRD Scores as Markers
High homologous recombination deficiency (HRD) scores indicate genetic instability and may predict which tumors respond to platinum-based chemotherapy, according to recent findings. A single-arm trial3
led by Melinda Telli, MD, showed neoadjuvant carboplatin, gemcitabine, and iniparib led to a 70% pathologic complete response in TNBC patients with high HRD scores, compared with 20% in those with low HRD scores. Investigators used a tumor DNAbased assay to identify underlying defects in the homologous recombination pathway.
Telli will head an upcoming phase II E5112 trial that will compare a neoadjuvant dose-dense doxorubicin/ cyclophosphamide/paclitaxel regimen with carboplatin plus gemcitabine. The primary endpoint will be invasive pathologic complete response (pCR) in the breast and nodes in the high-HRD group.
The optimal first-line chemotherapy for TNBC is a common question among clinicians, according to O’Shaughnessy. The phase III CALGB 40502 trial4
did not show a clear benefit from weekly 150 mg/m2
O’Shaughnessy described combined treatment with eribulin mesylate and capecitabine as another promising new regimen. One phase III study6
showed that patients with TNBC who took eribulin as a second-line therapy tended to have a longer overall survival (median 14.4 months) than those who took capecitabine (9.4 months), and O’Shaughnessy described a personal case study of a 30-year-old woman with metastatic TNBC who achieved a near-complete response after 10 months of treatment.
O’Shaughnessy indicated that eribulin may have an antimetastatic role that makes it particularly useful in drug-resistant TNBCs. According to a preclinical in vitro study,7
eribulin disrupts microtubules, which form the “scaffolding” of the cancer cell and enable it to travel to other tissues through the vasculature and metastasize. An exploratory analysis of the phase III trial data,8 presented by Edith Perez, MD, at the 2013 European Cancer Congress, suggested that eribulin tended to delay the development of new metastases in the lung, liver, and central nervous system longer than capecitabine did in patients with TNBC.
O’Shaughnessy added that learning how each of these drugs is involved in the MAPK (associated with proliferation) and PI3K (associated with metastasis) pathways will help clinicians prescribe the agents appropriately.
Another question involves the role of dexamethasone pretreatment; in a TNBC cell line (MDA-MB-231 cells) the use of the corticosteroid reduced paclitaxel- induced tumor cell apoptosis,8
which may be a critical concern in TNBC treatment, according to O’Shaughnessy.