Breast cancer is the leading cause among cancer deaths in India. Indian women are getting breast cancer at younger ages and more are dying of the disease than in other parts of the world.
For example, approximately 145,000 new cases of breast cancer were diagnosed in India in 2012 and nearly 70,000 women died from the disease. The survival rate over five years for women diagnosed with breast cancer is a poor 60% in India compared to more than 80% in western countries.
Oncologists have pointed to both the lack of awareness and the difficulty in treating late stage breast cancer for the unfortunate trend. But, there may be yet another factor. A new analysis of cancer literature from India shows that there is a higher rate of the most aggressive type of breast cancer, the triple negative breast cancer or TNBC, among Indian women than in other parts of the world.
Three kinds of breast cancer
Breast cancer cells typically have receptors for hormones like estrogen or progesterone or the human epidermal growth factor HER2. Oncologists prescribe anti-hormone treatments for hormone receptor cancers and drugs like trastuzumab for HER2 receptor tumors, often with good results.
Triple negative breast cancer cells lack receptors for all three. Hence the name. This makes this form of cancer resistant to conventional medicines and harder to treat, though certain types of chemotherapy have been shown to work against such tumors.
The new study by published by scientists from medical centers at the University of Pittsburgh and the University of Kentucky in the United States is a detailed examination of 17 breast cancer studies conducted between 1999 and 2015 in different regions of India. Published in the Journal of Global Oncology, the study shows that among more than 7,200 patients whose average age was 50 years, prevalence of TNBC was 31%. TNBC accounts for only about 12%-17% of all invasive breast cancers in Caucasian populations.
In fact, the rate of TNBC in India is comparable to the prevalence seen in African American women and is more than twice, sometimes thrice, the prevalence in other ethnic groups.
The combination of a high mortality due to breast cancer and the high prevalence of triple negative breast cancer is a double whammy in India, explained Aju Mathew of the Markey Cancer Center at the University of Kentucky and senior author of this study.
If a person is diagnosed early with breast cancer that is either hormone or HER2 receptor positive, the chance of the person surviving five years is about 90%. If a person is diagnosed with metastatic or Stage 4 cancer of these two varieties, the chances of that person surviving after five years is greater than 30%.
However, these survival rates drop drastically for triple negative breast cancer. Caught early, a patient has a 60% chance of surviving five years.
“If a patient is diagnosed with metastatic or Stage 4 triple negative breast cancer today, there is very little chance that the person will be alive in five years,” said Mathew.
Why do Indians have more TNBC?
The study’s authors attach several possible reasons for the this high rate of triple negative breast cancer among Indians from lifestyle factors like diet and obesity, to reproductive factors like having more than two children as well as socioeconomic factors that delay screening and treatment. However, there are indications of a genetic predisposition to TNBC among Indians.
“The next step is to do studies with patients diagnosed with triple negative breast cancers to see if these patient have some common genetic pattern or mutation that place them at a higher risk of getting triple negative breast cancer,” said Mathew.