Primary cutaneous lymphomas: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up.

Primary cutaneous lymphomas (PCLs) are defined as non-Hodgkin lymphomas that present in the skin with no evidence of extracutaneous disease at the time of diagnosis. After the gastrointestinal lymphomas, PCLs are the second most common group of extranodal non-Hodgkin lymphomas with an estimated annual incidence of 1/100 000. PCL must be distinguished from nodal or systemic malignant lymphomas involving the skin secondarily, which often have another clinical behaviour, have a different prognosis and require a different therapeutic approach. In recent lymphoma classifications PCLs are therefore included as separate entities. Within the group of PCL distinct types of cutaneous T-cell lymphoma (CTCL) and cutaneous B-cell lymphoma (CBCL) can be distinguished. In Europe, CTCLs constitute 75%–80% of all PCLs, CBCLs 20%–25%, but different distributions have been observed in other parts of the world.