SUMMARY: Breast cancer is the most common cancer among women in the US and about 1 in 8 women (12%) will develop invasive breast cancer during their lifetime. It is estimated that 266,120 new cases of invasive breast cancer will be diagnosed in 2018 and 40,920 women are expected to die from the disease. DNA can be damaged due to errors during its replication or as a result of environmental exposure to ultraviolet radiation from the sun or other toxins. The tumor suppressor genes such as BRCA1 (Breast Cancer 1) and BRCA2 help repair damaged DNA and thus play an important role in maintaining cellular genetic integrity, failing which these genetic aberrations can result in malignancies. The BRCA1 gene is located on the long (q) arm of chromosome 17 whereas BRCA2 is located on the long arm of chromosome 13. Mutations in BRCA1 and BRCA2 account for about 20 to 25 percent of hereditary breast cancers and about 5 to 10 percent of all breast cancers.These mutations can be inherited from either of the parents and a child has a 50 percent chance of inheriting this mutation and the deleterious effects of the mutations are seen even when an individual’s second copy of the gene is normal.
Breast cancer patients have a 5-12% lifetime risk of a second primary cancer. It remains unclear however whether patients with breast cancer and another primary cancer have mutations in genes other than BRCA1 and BRCA2, compared to those with a single breast cancer. There are well established data on the cancer risks, associated with different gene mutations. The authors hypothesized that among these patients, a number of factors including environmental exposures and genetic predisposition, may play a role in the development of more than one primary cancer in their lifetime. Recently published study suggested that there was a 85% cumulative breast cancer risk by age 60 years, among those with mutations in the TP53 gene (Cancer2016;122(23):3673-3681). Further with the increasing recognition that germline mutations in genes may have clinical and treatment implications, majority of patients are feeling comfortable opting for upfront multiple genetic mutation testing.
The researchers in this study looked at a panel of 15 actionable mutations beyond BRCA and the gene panel included TP53, PALB2, CDH1, PTEN, STK11, CHEK2, ATM, NBN, MSH6, PMS2, MSH2, MLH1, CDKN2A, MUTYH monoallelic, and CHEK2 Low Risk. Two cohorts of BRCA1 and BRCA2 negative patients were studied. The first cohort included high-risk breast cancer patients with either a single breast cancer (N=464) or breast cancer and an additional primary cancer (N=551). The second cohort comprised of patients with familial breast cancer (inherited risk) with either a single breast cancer (N=1464) or breast cancer and another primary cancer (N=340).
In a total of 891 patients in both cohorts who had breast cancer and an additional primary cancer, there was twice the risk of inheriting mutations in genes other than BRCA1 and BRCA2. In cohort 1, the mutation rate among patients who had breast cancer and an additional primary cancer was 8.7% compared to 4.1% among those with single breast cancer (P=0.003) and in cohort 2, the mutation rate was 8.2% versus 4.2%, respectively (P=0.003).
There was however a differences in individual gene mutation rates between the two cohorts. Among patients with breast cancer and an additional primary cancer in cohort 1, mutations in TP53 and MSH6 were significantly higher, whereas among the patients in cohort 2 with familial breast cancer, mutations in ATM, CHEK2 and PALB2 were significantly higher both in those with breast cancer and another primary cancer and those with a single breast cancer.
The authors concluded that patients with multiple primary cancers should be offered multiplex panel testing to identify patients at risk. Identifying mutations, especially mutations in the TP53 gene may have a bearing on appropriate recommendations such as risk-reducing bilateral mastectomy or mastectomy instead of a lumpectomy in this patient group. Thus, risk assessment using multiple genetic testing panels can be beneficial for clinical care and surveillance. Inherited mutations in breast cancer patients with and without multiple primary cancers. Maxwell KN, Vijai V, Lilyquist J, et al. DOI: 10.1200/JCO.2018.36.15_suppl.1503 Journal of Clinical Oncology 36, no. 15_suppl (May 2018) 1503-1503.
