No biopsy, diagnostic test is 100 percent accurate, but some are very close, and a direct biosy is one, but rarely, due to contamination, human error, inadequate discription, and not enough tissue section where biopsy was taken from, failures can happen. White patches, leukoparia, has many causes, and does not usuualy mean cancer as much as the red patches, erthoplakia, does, and id usually a concern. Although not used often in oral biopsies, a fine needle biosy can also be used to check for deep cancer cells, but the oral scapel biopsy is the gold standard. Good luck with everything.