Peripheral T-Cell and Natural Killer Cell Neoplasms

PERIPHERAL T-CELL AND NATURAL KILLER CELL NEOPLASMS

Peripheral T-cell lymphoma, unspecified is a “wastebasket” diagnostic category.

Adult T-cell leukemia/lymphoma (ATLL) is a malignant T-cell disorder (CD4-T cells) due to HTLV-1 infection. It is often seen in Japan and the Caribbean. Clinical symp-toms include skin lesions, hypercalcemia, enlarged lymph nodes, heptomegaly, and splenomegaly. Microscopically, characteristic hyperlobated “4-leaf clover” lympho-cytes can be found in the peripheral blood.

Mycosis fungoides is a malignant T-cell disorder (CD4+ cells) that has a better prognosis than ATLL. It can present with a generalized pruritic erythematous rash (no hypercalcemia), which develops as a sequence of skin changes:

inflammatory eczematous stage → plaque stage → tumor nodule stage

Microscopically, atypical PAS-positive lymphocytes are present in the epidermis (epidermotropism); aggregates of these cells are called Pautrier microabscesses. If there is erythroderma and cerebriform Sézary cells are present in peripheral blood, the condition is called Sézary syndrome.