San Antonio International Breast Cancer Conference

Every year at the beginning of December, an international breast cancer conference takes place in San Antonio, Texas. I remember attending the first such meeting about 30 years ago, when there were barely 200 participants. In 2019, more than 7,000 participants attended the meeting.

I am going to review two major presentations from San Antonio to provide you with an example of a key area of research exploration.

There is a lot of excitement about treating cancers with immunotherapy. Such treatment has been effective in lung cancer, melanoma and kidney cancer, but not breast cancer. However, recent immunotherapy research has targeted a specific sub-group of breast cancer patients.
About 10 to 15 per cent of patients present with a type of breast cancer called triple negative breast cancer (TNBC). It is called TNBC because it is negative for the estrogen receptor, progesterone receptor, and HER2 protein.

TNBC often is associated with a poor prognosis. The usual treatment is chemotherapy. Recent research has shown that the prognosis of TNBC correlates with immune infiltration, i.e. the greater the number of lymphocytes (a type of white blood cell which is an important part of your immune system) seen in the breast cancer tissue, the better the prognosis. Hence, perhaps immunotherapy can work in these cancers.

A clinical trial called MICHAELANGELO was conducted to test whether treatment with immunotherapy improves response to chemotherapy in patients with TNBC. Two hundred and eighty patients presenting with locally advanced TNBCs were randomly allocated to Atezolizumab (an immunotherapy drug) plus chemotherapy, or chemotherapy alone, both for 24 weeks. There was no difference between groups in the complete response rate, i.e. the complete disappearance of the cancer. This was what we call a “negative trial”.

In a second trial called KEYNOTE, 600 patients with newly presenting locally advanced TNBC were randomly allocated to Pembrolizumab (an immunotherapy drug) plus chemotherapy, or placebo plus chemotherapy. Treatment was for 24 weeks. There was a 14 per cent improvement, which was statistically significant, in favour of the immunotherapy group.

The results of these two trials presented in San Antonio are conflicting. Why? Possible explanations are: 1) the immunotherapy drugs and the chemotherapy given were different in the two trials; and 2) the trial with the positive result was much larger than the one with the negative result.

It is important to remember that the results of these two studies are preliminary. The outcome reported, i.e. complete response rate which assesses tumour shrinkage, is an early outcome and the patients need to be followed longer to see if the treatment impacts survival. So it is too early to determine whether immunotherapy plus chemotherapy should be used in regular clinical practice.