loose stool may be due to infection or hypersecretion so detailed history required.black stool cant be due to rectal or anal cancer
. black tarry stool should be due to upper G-I bleed and that can be a cause of collapse. so stool exam to be done , if necessary blood transfusion
will be needed. anyway anorectal cancer
can be treated by chemoradiotherapy
first, if not metastatic disease. then surgery may be tried.first go for conservative management at a good hospital then think about definitive management.