I stayed out of work for just over a year. It really was at my bosses discretion . Then I went back to work for a month and left again for reconstructive surgery... I was gone for an additional 6 months ( new boss) and new boss gave me a hassle but it was in regards to me retaining my seniority and a few other things. I fought them and retained everything.

@A MyBCTeam Member
If you're feeling great, it might feel good to go back to work. For me, it was a great feeling to go back to my old life, take time off for surgeries, and then go back to work again. There's a lot to be said for having to focus on things other than cancer treatment.

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A MyBCTea...

When my oncologist filled out my state disability form he stated I would be off work from April 9 2015 to Jan 1, 2016 I provided to employer along with FMLA forms, it was then extended to April 1 2016 ,employer agreed to the extention, but then again my union reps were involved in speaking to employer about saving job for me,check your state employment laws and federal one too, and maybe speaking with boss, ultimately they will be the deciding factor

I was approved for what they call long term disability after 6 months. Radiologist approved for while going through radiation.

My previous employer extended my leave from the federally required 12 weeks of FMLA, to 14 weeks. I did not have to submit a special request for the extended leave as they knew I would be returning very soon; however, some companies do require it and have to approve it. They have to determine if there will be any "undue hardship" without you there. If there is, such as others carrying a heavier work load or deadlines getting missed, they could refuse your request and it would be completely legal.
You may qualify for Americans with Disabilities Act (ADA) where your employer would have to offer you "reasonable accommodations" to do your job... Like working from home or reduced hours.
I hope your HR department (and company, as it truly is their policy) is willing to help you while you continue to recover. It's not fair that as we try to heal and get well, by keeping our stress level down, resting, and relaxing, our employers do not allow us the opportunity to get well, as we have to worry about things like job security.
Many prayers for you, as you continue through your treatment and recovery. I wish you the best!