usually i read the wikipedia articles about the disease and the common treatments, a couple dozen papers starting from google scholar via pubmed and sci-hub, maybe a relevant medical textbook via libgen. also talk to family members and friends about the issue. you can also find papers in medical journals and the mmwr on the prevalence of possible complications from different kinds of biopsies

this takes a little longer than undergoing the biopsy, but it's enormously more pleasant, and it lets you know when doctors are ignorant or lying, which is perhaps even more important information. it's orders of magnitude easier than undergoing chemo and radiation so i don't know why 'eager but uneducated' laypeople don't always do it. maybe they're too used to living in a world without sci-hub and libgen

it's also easier when it's not the first time

it's never impossible that any part of your body could be cancerous, so 'super unlikely to be cancerous but it's not impossible that it could be' is a terrible justification for taking action