Remember, Doctors have the ability to use off label based on their own training and experience. They can be the first one to off label use (FDA Approved Drugs) without others to follow.
If Botox can be used to fight migraines, initially off label; Keytruda should be allowed if traditional methods and means have failed. Also, the FDA has recently approved things such as Keytruda as part of the "Right to Try" rules. The FDA has approved the drug, but clinical trials have not yet determined how good it is and its use for certain circumstances.
These two things should help your doctor make the best decision for your treatments.
D/H 47 years old, 10/2014, Stage IV M/CRC, nodes 12/15, para-aortic, 5 cm sigmoid resection, positive Virchow. KRAS mut, MSS, Highly Differentiated, Lynch Neg, 5FU/LV and Avastin 1 YR (Oxi for 5 months), Zeloda/Bev since 01/2016. 02/2019 recurrence para-nodes, back to 5FU/LV Oxy/Bev. It is working again. "...Perseverance is not a long race; it is many short races one after the other."-Walter Elliot