After encouraging results in treating melanoma, lung and kidney, immunotherapy enters the realm of gastric malignancies.
The FDA has approved Pembrolizumab, (Keytruda) by Merk, for use as a third-line treatment for locally advanced or metastatic adenocarcinoma of the stomach and gastro-oesophageal junction that express programmed death receptor-ligand 1 (PD-L1).
Immunotherapy tries to elicit the mechanisms how cancer cells can hide from the immune system. It aims to help our immune system in recognising a tumour and facilitating the natural immune response that is believed to be more efficient than any drug could ever be.
What is PD-L1
PD-L1 is a molecule that can be found on cancer cells, it binds with PD-1, a receptor present on T cells and therefore plays a role in immune regulation. When the two molecules bind they transmit an inhibitory signal that reduces the proliferation of T cells or even causes their death; in other words, PD-L1 tells the immune system not to bother attacking it.
How does Pembrolizumab work?
The concept of PD-L1 inhibitors is to block this molecule and thus prevent it from binding to the T cells. In other words, blocking the inhibitory effect in order achieve activation of the immune response.
The results so far
Taking into account that this is treating a third-line gastric cancer, the figures for 6- and 12-month duration of response are not mind blowing but show some promising features. Larger numbers will help to get a clearer picture in the future.
Immunotherapy in solid tumours is always going to be harder to achieve, especially in the advanced stages. It will be interesting to see what results can be reached when using PD-L1 inhibitors in combination with other treatments and also how it will fare as an early treatment.