Is colostomy necessary?

I was diagnosed with anal cancer in March of this year and underwent 6 weeks of chemo radiation treatment ending in May 2024. I handled treatment fairly well. In September I was pretty much pain free but bm was still radical. Pain started returning in October. Visit to my colorectal surgeon showed an ulcer in the area of the tumor. I went through a sigmoidoscopy two days ago 12/5/24. Dr did another biopsy and is saying if cancer is still present he will need to perform a colostomy.  I am wanting to find out if there are other options and what options there may be if there are not cancer cells in this biopsy.