This page has been written by : Radhika Nair
MOLECULAR PROFILING
What is 'Molecular Profiling'?
Remember the concept that genes (physically present as DNA) are transcribed and translated into proteins? So you can imagine that if tumors express different proteins, they have different genes too. Scientists have developed techniques by which we can determine the mRNA (which are the molecules that convey the message from the DNA to the proteins) produced by a tumor cell. This allows scientists to build a "signature" of the molecules in a cell which is called a molecular profile.
Based on the molecular profiles, tumors can be classified into different breast cancer subtypes. This is important for a patient as women with different subtypes of breast cancer can have different prognosis and survival times. See the graph below which shows you the survival times associated with different subtypes of breast cancer.
Based on the molecular profiles of tumors from breast cancer patients, scientists have classified breast cancer into 5 major subtypes-
Luminal A
Luminal B
HER 2 Enriched
Basal Like
Normal Like
Importantly, depending on the subtype, the average survival time and therapeutic options differ. For example, luminal A subtype have good prognosis with Tamoxifen treatment with over 90% women surviving 5 years post diagnosis.
Is molecular profiling useful or is it just another cool technique?
The reason why understanding the entire molecular make up of a cell is important is because it has clinical consequences for patients to identify targets which can be drugged and used to kill cancer cells. While there is a long way to go in making full use of the vast amounts of data being generated from thousands of tumors from breast cancer patients and use it to develop "personalised" therapies (meaning tailoring drugs to each individual patient with maximum benefit and minimal side effects), it is a start.
Based on molecular profiles obtained from breast cancer samples, genes have been identified which are expressed in tumor cells differently when compared to normal healthy cells. This differential expression of genes forms the basis of some diagnostic tests like Oncotype DX®. Patients with tumors that express the Estrogen Receptor and are node negative (that is there are no detectable cancer cells in the lymph nodes) can benefit from this test which allows clinicians to determine the need for chemotherapy with Tamoxifen.
The problem with these tests is that they are not necessarily correct for all patients and are also very expensive. In addition, we have to keep in mind that these are based on studies done in the West and the molecular profiles for Indian patients might be different. The promise of genetic personalised medicine is very powerful especially for women who present with breast cancer which can't be treated with current therapies effectively or in which the tumor cells have spread to other parts of the body (metastasis). This is especially relevant to India where we are noticing an increase in younger women presenting with aggressive forms of the disease (see section on statistics?) which don't have targeted therapies. The explosion in genomics which has resulted in huge databases like TCGA (The Cancer Genome Association) allows scientists to now interrogate or understand the genetic basis of breast cancer better. Keep an eye on this space to keep up with the exciting developments occurring in this rapidly evolving field!