Proliferative verrucous leukoplakia and its related lesions.

Proliferative verrucous leukoplakia (PVL) is a unique type of clinical oral leukoplakia. Enigmatic in etiology, PVL behaves in a far more aggressive fashion than other forms of leukoplakia. Its aggressiveness relates not only to a high recurrence rate, but more so to a very high level of and relentless progression from a localized simple keratosis to extensive oral disease and squamous carcinomas of verrucous, or conventional squamous cell type. Diagnosis is often late in the protracted course of PVL with the disease in an advanced stage when it is especially refractory to treatment. Within the histologic spectrum that is seen in PVL, usually as a function of time, are: (1) verrucous hyperplasia (VH), a histologically defined lesion; (2) varying degrees of dysplasia; and (3) three forms of squamous cell carcinoma: verrucous, conventional and, according to some, papillary squamous cell carcinoma. Each of these are discussed both within and outside the context of PVL. VH is a forerunner of verrucous carcinoma and the transition is so consistent that the hyperplasia, once diagnosed, should be treated like verrucous carcinoma. VH is not only an oral lesion; it can occur in the upper airway (sinonasal tract and larynx) where it is not usually found within a maternal soil of PVL. Papillary squamous cell carcinoma has been a loosely defined neoplasm, more often considered a verrucal type of malignancy. It nonetheless is a distinct clinicopathologic entity, separate from verrucous carcinoma and without a predilection for the oral cavity or an association with PVL.