A precancerous condition (or premalignant condition) is a generalized state associated with an increased risk of cancer. If left untreated, these conditions may lead to cancer. Sometimes the term "precancer" is used to describe carcinoma in situ, which are non-invasive cancers that are technically "cancers," but have not progressed to an aggressive, invasive stage. Not all carcinoma in situ will progress to invasive disease.
Premalignant lesions are morphologically atypical tissue which appears abnormal under microscopic examination, and in which cancer is more likely to occur than its apparently normal counterpart.