August 2013 Ask the Expert: Triple-Negative Breast Cancer Highlights
Dr. Anders: Following traditional chemotherapy, surgery, and radiation therapy for TNBC, leading a generally healthy lifestyle is a proactive way to help reduce the risk of recurrence and to ward off other illnesses. Studies have shown that regular exercise (approximately 5 times a week) and a healthy diet full of fruits and vegetables (5 servings combined) may reduce breast cancer recurrence. A large retrospective study of aspirin use also showed that routine use may be linked to lower breast cancer recurrence and, if already on it for cardiovascular health, it is very reasonable to continue. The data for metformin is somewhat mixed, but some retrospective studies have shown a protective effect of metformin on breast cancer risk.
Dr. Anders: Studies have shown that women with TNBC have twice the rate of distant recurrence as compared with other types of breast cancer. In contrast to other subtypes of breast cancer, the risk of TNBC recurrence peaked within 3 years of diagnosis and declined rapidly thereafter. These studies are somewhat limited by their retrospective nature and use of older, possibly outdated, chemotherapy regimens.
Dr. Anders: In general, TNBC accounts for approximately 15 – 25 percent of all breast cancers and is over-represented among younger women and African-American women. Awareness of TNBC is certainly increasing, but to my knowledge, the incidence of the disease is not.
Dr. Anders: At present, the standard of care for TNBC in the adjuvant setting is chemotherapy. Unfortunately, the addition of the anti-VEGF antibody, bevacizumab, to standard adjuvant chemotherapy in the BEATRICE trial did not yield improved outcomes. Basic scientists and clinical researchers continue to evaluate other pathways that may be of benefit in this setting.
Dr. Anders: Presently, there is no clinical test to differentiate luminal vs. basal-like TNBC. The PAM50® assay, which is a gene-based assay predictive of breast cancer subtype, is being used in the research setting; however, it is not yet clinically available. One study indicated that close to 40% of cancers that are estrogen receptor/progesterone receptor “low” (as defined as 1 – 10% staining) are actually luminal breast cancers. Until we have additional tools available in the clinic, the ability to predict luminal vs. basal-like TNBC is restricted to the research setting.
Dr. Anders: While the rates of pathologic complete response to chemotherapy for TNBC vary by study, rates have consistently been in the 30 – 40% range. Many studies have illustrated a higher pathologic complete response to chemotherapy for TNBC as compared with other subsets of breast cancer, particularly hormone-sensitive breast cancers.
Dr. Rugo: Next-generation sequencing is used to evaluate acquired or somatic gene mutations in cancer cells. BRCA1 and BRCA2 mutations are germline mutations. In other words, they occur in the cells you are born with. Because next-generation sequencing evaluates changes in cancer-related genes, this testing might pick up an unknown germline BRCA mutation as well, although it this not the standard screening test for the BRCA inherited mutations.
Dr. Rugo: AE37 is a modified HER2 peptide, or small protein that is linked to an immune stimulant, GM-CSF, to create a vaccine. It has been tested in a clinical trial compared to a different unmodified peptide and to GM-CSF alone in patients with high-risk, early-stage breast cancer that have some expression of HER2. Notably, the cancers can have minimal expression of HER2, but not meet the standard criteria for HER2 positivity. Preliminary studies with this vaccine are promising, but we need the data from the clinical trial described above in order to really understand the promise of this new vaccine approach. Results should be available in 2014.
Dr. Rugo: STK11 (also known as LKB1 or liver kinase B) is a gene that makes an enzyme called serine/threonine kinase 11. This enzyme functions to suppress tumor development. Mutations that cause loss of function in this gene result in the Peutz-Jeghers Syndrome, which is associated with an increased risk of developing a number of different cancers as well as polyps in the bowel. Although breast cancer risk is increased in patients with Peutz-Jeghers, this represents a very, very small fraction of all breast cancers.
Interestingly, recent research has identified a large number of somatic or acquired mutations in the STK11 or LKB1 gene, and these mutations have been found in a number of common cancers including lung, cervical, breast, intestinal, testicular, pancreatic and skin cancers. This is now of interest as a possible target for treating cancer, or as a marker to predict response to specific targeted therapies.
Dr. Rugo: It appears that the risk of recurrence is relatively similar regardless of whether you are born with a mutation in a BRCA gene. The risk of developing a new breast cancer is higher in women with BRCA mutations, but this does not affect the risk of having an already-diagnosed cancer return in other parts of the body. Recent data suggest that cancers with BRCA mutations may be more sensitive to specific types of chemotherapy or novel agents that cause damage to tumor cell DNA or prevent repair from chemotherapy-induced damage, but this is still being confirmed in ongoing research.
Dr. Rugo: One randomized study that evaluated the effect of diet change on outcome after breast cancer suggested that lower intake of fat could be associated with less recurrence. However, women who adhered to a lower intake of dietary fats also lost weight, which might also have a positive effect on recurrence risk. Another large study that evaluated a diet high in fruits and vegetables compared with standard dietary information found no difference in risk of recurrence. A diet with a lower intake of saturated fats has many health benefits, so is recommended regardless of whether a person has been diagnosed with breast cancer. Olive oil is a healthy form of fat that does not appear to be harmful in the amount usually ingested in the diet.
Dr. Rugo: The prognosis of TNBC is related to the extent of cancer at diagnosis, and the biology of that cancer, which determines its responsiveness to chemotherapy. The BRCA mutation may make these cancers more sensitive to chemotherapy agents that damage tumor DNA, but it appears that a number of TNBCs without BRCA mutations are also sensitive to these chemotherapy agents. Researchers are working on a test to try to figure out which TNBCs are more sensitive to specific types of chemotherapy. At the present time, prognosis appears to be similar regardless of whether the TNBC is associated with an inherited mutation in a BRCA gene or not.
Dr. Rugo: Most but not all BRCA1-associated cancers are triple-negative, but a proportion are estrogen receptor-positive. The same is true in reverse for BRCA2 mutations: most cancers are estrogen receptor-positive, but some are triple-negative. Treatment and follow-up should be based on the biology of the diagnosed cancer, not only the BRCA mutation. Prevention or prophylaxis is based on the risks associated with the inherited BRCA mutation.
The best sources of information are the NCI website, the American Cancer Center, LBBC, and others.