ABSTRACT
INTRODUCTION Invasive malignant neoplasms of epithelial and melanocytic histogenesismay arise from preexisting noninvasive intraepidermal or in situ malignant lesions. These lesions have been known as premalignant lesions or precancers. The concept of skin precancers has been revisited recently. The controversy lies primarily in whether the lesions that had been previously recognized both clinically and microscopically as noninvasive tumors should be regarded as early invasive cancers and treated accordingly, due to their potential to develop invasion into the underlying or adjacent dermal stroma, if left untreated. It is widely accepted that in situ (noninvasive) malignant neoplasms are curable by early detection and complete excision, whereas invasive tumors require more aggressive and destructive chemotherapy as well as radiation. Although de novo invasive carcinomas do exist, the majority of epithelial and melanocytic tumors undergoes cytologic evolution (malignant transformation) under the influence of chemical carcinogens and other carcinogenic factors, through intraepithelial nuclear DNA alterations, and eventually breaks through the epithelial-stromal junctional zone, to become an invasive lesion capable of metastasis.
