Upon diagnosis of breast cancer (invasive ductal carcinoma) one of the first set of tests that is done is testing for estrogen receptor(ER), progesterone receptor (PR) and HER2 receptor. Based on the results of these immunohistochemistry (protein marker based) tests,breast tumors are classified into three categories-ER positive, HER2 positive and triple negative breast cancer (TNBC). There are numerous chemotherapy regimens used in breast cancer, however in certain cases, targeted therapy i.e. drugs that act against specific proteins that are either mutated or highly expressed in breast cancers, are also used.

ER positive disease is often characterized by mutations in a gene called PIK3CA.  A drug that targets these mutations has been shown to be effective in such cases.  This drug may be considered by your physician in late stage ER positive breast cancer. Genetic profiling can determine whether your tumor has such a mutation and whether it is a good candidate for PIK3CA targeting drugs,

Hormonal therapy is usually prescribed for ER positive disease post surgery in the adjuvant (add-on) setting. Studies have shown that such treatment is effective in controlling the disease. However unfortunately in certain cases, there is disease progression upon treatment with hormonal therapy. One of the most common ways in which this happens is when there are new mutations (acquired resistance) in the ESR1 gene (which is the target of hormonal therapy) which allow it to promote the growth of cancer cells even in the presence of hormone therapy. In such cases, profiling a tumor to confirm the presence of these mutations and switch to another therapy, is useful.

HER2 negative disease can be treated with a variety of regimens. One of the regimens under consideration in metastatic HER2 negative disease is treatment with a class of targeted therapy known as PARP inhibitors. PARP inhibitors affect the DNA synthesis and repair pathways in a cell and it has been found that mutations in genes that are involved in repair of DNA when it is damaged (the homologous repair pathway-most notable within this family are the BRCA1 and BRCA2 genes) render sensitivity to them

Sometimes a tumour, despite being given appropriate treatment, does not respond well to the therapeutic regimen. In such cases you and the clinician might want to consider other targeted therapy options if available. It may be useful to profile these tumours with a broad large panel of genes that are mutated across a variety of cancers as there may be a possibility that one of them is also mutated in your tumour. If such a gene is identified, it may open up additional avenues of treatment with targeted therapy. Hence,you and your doctor may consider Strand’s large panel genetic tests for such cancers if you would like to explore other potential treatment options. Large panel testing can also help determine your suitability for immunotherapy by measuring the Tumour Mutational Burden (TMB) and Microsatellite Instability (MSI). Both these are a measure of the immunogenicity of the tumour i.e. how well it can be recognized and attacked by the immune system. Large panels can also be used at the outset if you are interested in comprehensively understanding a tumour’s genetic makeup before starting treatment.