Breast Cancer- Targeted therapies

Breast Cancer- Targeted therapies

This is the first of a four-part series on targeted therapies in breast cancer. Over the series, we will cover the current and next generation treatments for the different breast cancer sub-types; HER2 positive, HER2 negative and triple negative breast cancer.

In this first part, we introduce the series by looking at the prevalence and survival rates of women with breast cancer including breast cancer subtypes and current treatment overview.

Epidemiology and prevalence

Breast Cancer is among the most common cancer in women worldwide - affecting around 12% of all women in the US, with more than quarter of a million new cases diagnosed in the United States in 2017. According to the World Health Organisation, an estimated 627,000 women worldwide died in 2018 due to breast cancer, with almost 50% of breast cancer cases and 58% of deaths occurring in less developed countries. Rates are increasing in nearly every region globally. When newly-diagnosed, most patients have two surgical options: breast conserving surgery with radiotherapy, or mastectomy. These are usually combined with some form of chemotherapy, and survival rates can be good. When diagnosed at an early stage, for example, 5-year survival rates are almost 90% in the UK. However, the 5-year survival rate for patients with metastatic disease remains low, at just 27% for US women and about 16% for UK women. Survival rates also depend on the subtype of cancer.

Subtypes of breast cancer

At the moment, breast cancer is categorised into major subtypes based on the presence or absence of molecular receptors. The subtypes are hormone receptor positive or negative (oestrogen ER and/or progesterone PR receptors), and human epidermal growth factor receptor 2 (HER2 or ERBB2) positive or negative. Cancer cells that do not have any of these three receptor types (ER, PR or HER2) are called triple-negative.

​

​An understanding of these subtypes has led to a new generation of therapies designed to specifically target different forms of breast cancer. For example, hormone receptor positive cancer cells that depend on oestrogen for growth can be treated with drugs to block oestrogen effects, such as tamoxifen. Hormone receptor positive breast cancer generally has a better prognosis, and represents some 84% of patients. HER2 negative tumours represent about 70% of these patients. HER2 positive breast cancers, representing 15%-20% of patients, are generally more aggressive than HER2 negative tumours, but respond to drugs such as> Herceptin (trastuzumab) from Genentech/Roche, in combination with conventional chemotherapy. The approval of this drug has improved the prognosis for HER2 positive patients significantly. The most challenging to treat - triple negative breast cancer - is observed in about 15% of patients. As genetic analysis of tumour cells improves, other treatable subtypes are emerging, including tumour cells with BRCA1 or BRCA2 gene mutations.

Parts 2,3 and 4 are now available for HER2 positive, HER2 negative and Triple negative breast cancer respectively.