I was diagnosed with multiple myeloma about 5 years ago, and went through about 6 months of nasty infusions before settling into some drug therapies that have been able to keep things in check. My prognosis is good, but the drugs are crazy expensive, and will hopefully continue to be covered through my health insurance, including eventually Medicare (if it's still around).
My oncologist was the first medical professional that I came out to (besides my endo, of course), and he's been so supportive, almost giddy when I made my first visit after transition. I think I'm his first trans patient, and he's been researching topics of interest and passing on his discoveries to us each time we visit. When my mother questioned whether my transition was going to lower my chances of surviving cancer, I was able to tell her that high-dose estrogen was previously used as a prophylaxis for prostate cancer, so transition actually improved my chances of surviving cancer (I enjoyed throwing that one out there

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Good luck with your own journey. I'm always optimistic about cancer prognoses, as there is so many great research studies going on, with breakthroughs coming out all of the time. Whenever I think about having cancer, I feel like everyone has got some kind of cancer in them, and getting the diagnosis is, in a sense, a blessing compared to all of the people who never know what cancer lurks within. I hope that the surgery is compatible with your transition plans. I imagine that being able to complete your transition may be the best boost to your system, letting you live fully as your authentic self.
Erin