I had the same concern...about waiting, and giving the melanoma a chance to grow while "Waiting" to see if the keytruda did anything. I did the adjuvant keytruda therapy. Basically if you do some research they say there is a better survival rate for melanoma reoccurance for those who took the Immunotherapy therapy for 3 injections and left the tumor in, than those who took out the tumor, then did the Immunotherapy therapy.
I guess this way, they can monitor the tumor to see if it has an effect on it, if it continues to grow or shrinks. After 3 injections I went ahead and took out the second tumor through surgery. At the follow-up, it appears the immunotherapy had a minimal effect on the tumor. About a 4% response rate. Not too promising. But an effect non the less. My last MRI scan after the theropy didn't find anything, but the pet scan did. A very very small trace of what could be considered melanoma in the same arm. Too small to cut out when they cut out the other. They couldn't find it to try to remove it. But my last scan about 3 weeks ago didn't find anything. It was an MRI, not a Pet, which doesn't find the small stuff. In fact, I visually found my other melanoma about 1 inch from the first one on my arm, where the MRI scan didn't even pick it up. You need to be on your game and visually check yourself frequently. Nodular melanoma sneaks up and grows very fast. I know!
I wish you Gods Speed!