Hello and thanks for your enquiry,

It is completely understandable to feel worried about switching from pembrolizumab (Keytruda) to chemotherapy tablets, and having to stop pembrolizumab early due to side effects is quite common, and your oncology (hospital cancer team) team will have worked out the best plan for you moving forward.

Pembrolizumab does not attack cancer cells directly; instead, it retrains your immune system’s T-cells to recognise and destroy them. Clinical studies show that once the immune system is "switched on" by immunotherapy, that anti cancer response can persist in the body for a very long time, even after the drug is stopped.

People that develop immune related side effects, like your underactive thyroid (hypothyroidism) and adrenal insufficiency is noted in clinical studies with a highly active immune response against the cancer. It means the pembrolizumab successfully woke up your immune system.

Chemotherapy tablets work through a different path than pembrolizumab by directly stopping cancer cells from dividing and growing. The chemotherapy drugs are given to catch any remaining cancer cells, whilst stopping the immune driven inflammation that affected your endocrine glands. Developing an underactive thyroid and becoming steroid dependent due to adrenal gland changes, are known side effects of pembrolizumab, which can sometimes be permanent. This does mean that your body now requires medication for the hormones thyroxine and cortisol. Fortunately, at least, these conditions are manageable with daily medication.

I hope this helps,

Best wishes,

Vanda