Breast cancer has 10 sub-types: Study

Researchers analysed the DNA and RNA profiles of all these tumours and concluded that they constituted novel sub-groups with distinct clinical outcomes.

Written by Abantika Ghosh | New Delhi | Published:April 20, 2012 12:15 am

Reinforcing the impression that cancer is really many diseases,researchers in the United Kingdom,Canada and Norway have reported in the journal,Nature,that breast cancer has ten different sub-types — in terms of the constitution of the cells and the genetic mutations driving their changes — and future treatment should be developed for each of these rather than trying to evolve a one-protocol-fits-all model.

The study — a collaborative effort of Cambridge University,University of Oslo,King’s College among others,along with the METABRIC Group — analysed the genomic structure and cellular patterns of 2,000 breast tumours. All patients had been diagnosed 5-10 years earlier and their survival was mapped to understand if some breast cancers were less life-threatening than others.

Researchers analysed the DNA and RNA profiles of all these tumours and concluded that they constituted novel sub-groups with distinct clinical outcomes. There were some sub-groups that responded to oestrogen because of the presence of its receptor in the cells and others where the aberrations in the gene copies were such that they were more vulnerable to some drugs,so that the prognosis of these tumours is always better. Some forms of the disease had been triggered by drastic changes in the gene sequence of the cells (mutations),while others were missing entire sequences of genes present in normal cells (deletions).

The idea that cancer is many diseases is not new in the scientific world. Dr Siddhartha Mukherjee,in his Pullitzer-winning The Emperor of All Maladies — A Biography of Cancer,had dealt with it extensively. This is,however,the first time that a cancer of one particular part of the body has been so clearly classified at the genome level,opening new vistas for treatment.

“The study re-affirms cancer’s status as a mysterious disease and makes it clear why it is such a difficult disease. Earlier this month,the New England Journal of Medicine carried an article on how,when researchers sequenced four quadrants of a breast and a kidney tumour,all four areas of each of them turned out to be different. The catch for developing future targeted therapies is in identifying the driver mutation and then targetting it,” said Dr Shyam Agarwal,consultant oncologist at Sir Ganga Ram Hospital.

A driver mutation is mutation that triggers all the other changes in the genome of a cell that make it behave in the manner of a cancer cell. According to Dr P K Julka,professor of clinical oncology at AIIMS,onco-typing is one test done even now while treating breast cancer to decide the treatment module,but such minute sub-typing was not known earlier.

“They have broken the known sub-types into smaller groups. What this means is that cancer medicine will need to be more personalised. At present,we know about five types of breast cancer and,based on their risk profiles,we decide whether to do merely hormone therapy or start chemotherapy too,” said Dr Julka.

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