Hydroa vacciniforme-like lymphoma (HVLL) is a rare malignancy primarily of late childhood, adolescence, and early adulthood manifested cutaneously as a severe, recurrent, and prolonged photodermatitis. It represents the malignant end of a disease spectrum that includes classic hydroa vacciniforme (cHV) and hydroa vacciniforme-like lymphoproliferative disorder (HV-LPD). Similar to cHV, the etiology of HVLL involves an interaction of an immunological / infectious component, chronic Epstein-Barr virus (EBV) infection, and exposure to ultraviolet (UV) radiation, in which both UVA and UVB have been implicated. Certain individuals fail to develop immune tolerance to EBV infection and instead progress to chronic active EBV (CA-EBV). With repetitive UV exposure, the immune response progresses to one of a monoclonal atypical EBV-positive T cell population resulting in HVLL.

While cHV is a self-limited condition of children and early adolescence marked by pruritic papulovesicles and bullae confined to sun-exposed areas, both HV-LPD and HVLL present as atypical and severe forms of HV with increasingly frequent and severe recurrences, a more prolonged course extending past the normal age that cHV tends to remit (late teens), and the presence of systemic findings. These patients have facial edema, vesiculonecrotic and hemorrhagic lesions, and more severe scarring. Systemic findings include fever, hepatitis, hematological abnormalities, lymphadenopathy, and hemophagocytosis. Oral lesions and ocular inflammation including conjunctivitis and keratitis may occur. A coexisting hypersensitivity to mosquito bites has also been reported. As disease severity increases, lesions develop on areas of the body not directly exposed to sunlight.

Some studies indicate no apparent sexual predilection, while others favor a slight male predominance. Patients with HV-LPD from Asia and Latin / South America are reported, in small studies, to have more severe HV-LPD and higher rates of progression to HVLL than are those from Europe and North America.