Has anyone else discovered an autoimmune disorder with their cancer?

I was a stage 0 at 44 years of age. I didn’t take it as seriously as I should have. At that time the oncologist decided to do nothing. At the appointment I was trying to be really proactive and wanted double mastectomies. But my oncologist said -you seem really healthy all you need to do is have mammograms 1-2 times a year. I walked out of there thinking great. Fast forward 8 years and I had full blown stage 3c metastatic breast cancer. Exact spot where the stage 0 was at- left breast. Now I was looking mastectomies, 5 months chemo, radiation, Zometa and hormone blocker. Another 5 years go by and I have a grapefruit size tumor in my sacrum. 10*pain in my lower back. Placed on ibrance, Zometa and Letrozole. 2 1/2 years go by and finally they find out I have an autoimmune disorder called CVID. My body does not make plasma. Plasma helps to make immunoglobulins which mark cancer cells for your t-cells to fight. Which is genetic. So way back when I had a 0 stage that was really due to my autoimmune disorder. That went undiagnosed when my oncologist thought I would be fine. The question is why did my body make a bad cell and body did not fight it off 18 years ago. I am now NED. Only on Letrozole and Xembify (plasma). But it has been a long 18 years. So really make sure you do not have something secondary going on with your immune system. My question is - is there anyone out there that found they had an underlying condition. Like an autoimmune disorder with there metastatic breast cancer?