Despite the improvement in therapy in most of the non-Hodgkin lymphomas, the scenario for advanced-stage mycosis fungoides/Sezary syndrome remains unmodified. Allogeneic stem cell transplantation is still the best option to maintain a durable response, but it requires previous good control of the disease, and it is associated with several complications which could be related to therapies.Here we report a clinical case that pictures all the critical aspects of this rare and aggressive lymphoma: diagnosis and classification, selection of therapy, decisions based on comorbidities and tumoral modifications, and disease monitoring during therapies.We found that, besides comorbidities and tumor characterization, the detection of tumoral cells and other immune cells by flow cytometry along the disease could help to improve therapy selection and also to understand disease evolution.