Assessing the blood in T‐cell lymphoma of the skin

Linked Article:   Vermeer et al . Br J Dermatol 2021; 185 :19–25. A lymphoma is a cancer of lymphocytes, cells that form part of the immune system. One type of lymphocyte that can become cancerous is the T‐lymphocyte, or ‘T‐cell’. Cutaneous T‐cell lymphoma (CTCL) is a form of lymphoma that originates in the skin, and the two subtypes we know most about are mycosis fungoides (MF) and Sézary syndrome (SS). MF is the commonest sub‐type whereas SS is much rarer. One criterion for diagnosing SS is finding significant numbers of abnormal lymphocytes in the bloodstream, as in leukaemia. Most patients with MF do not have this finding, but the outlook is worse if they do. This review from the Netherlands, Germany, the UK and Italy stresses the need to accurately assess the blood in CTCL: for making a diagnosis, estimating severity and outlook, deciding on treatment and evaluating results, and comparing different treatments with each other. In the past, estimating the proportion of abnormal (neoplastic) lymphocytes in the bloodstream was done by looking down a microscope at a blood film and simply counting the lymphocytes seen to have the abnormal features. A more sophisticated method is to use flow cytometry, which is now recommended in international guidelines. This may be even more accurate when combined with a technique that looks at alterations in the genes of T‐lymphocytes. Researchers are looking at standardizing results from these techniques in order to compare them. The authors also mention that relatively little is known about blood involvement in early MF, which may be important.