At times i have to strain for a bm. at times somewhat less difficult. my bowel habits have changed and i have to wipe much more often. often underwear is soiled. stool looks brown with no visible blood. is this cancer? how might this be treated?

With any change in bowel habits you should be evaluated. You likely need to see a GI doctor. The only way to know if you have cancer is to do a colonoscopy, which you should have if you have never had one. By your description, it is difficult to stay exactly what the problem is so see a GI doctor for evaluation and treatment, if needed. Good luck!