I looked through my blogs to try and find the lymphedema references, and I couldn't find it! Here's a link to get started. I have known many people that have recovered from it. www.mayoclinic.com/health/lymphedema/DS00609
I still get regular massages and did during treatment. Whatever supports your body and your spirit will , I believe, help you heal. We are all so different that there isn't just 'one way', but there are many avenues to try.
Welcome to Yoga Bear! I blog for YB and wrote about lymphedema, there are options!
Gentle yoga may be very helpful, as long as the doctor agrees that it is alright to start. Many of my students find relaxation and passive stretching a way to access shoulder muscles. We are all so different.
I'm glad that you found YB and you will find much information to help you get started in yoga.