Background The coexistence of mycosis fungoides, a peripheral T-cell lymphoma, and B-cell malignancies or Hodgkin's lymphoma in the same patient is unusual. Most descriptions are isolated case reports and case series are strikingly sparse.
Objectives To detect cases of mycosis fungoides associated with B-cell malignancies or Hodgkin's lymphoma and to analyse the characteristics of and the interplay between the lymphoproliferative neoplasms.
Method Patients with mycosis fungoides who had B-cell malignancies or Hodgkin's lymphoma were selected from among 398 patients either treated or followed up in two tertiary medical centres during a 7-year period.
Results Eleven patients with mycosis fungoides and B-cell malignancy were detected (seven of non-Hodgkin's lymphoma, three of chronic lymphocytic leukaemia, one of multiple myeloma). No case of Hodgkin's lymphoma was found. In seven patients the mycosis fungoides preceded the B-cell malignancy whereas in four it was the B-cell malignancy which occurred first. The time elapsed between onset of the two malignancies ranged from 4 to 22 years (average: 12 years). Patients who had mycosis fungoides as the first neoplasm presented with earlier stages of mycosis fungoides (four of seven: IA, three of seven: IB) than those who had mycosis fungoides as their second neoplasm (of four, one: IB, one: folliculotropic, two: IIB). Among the four patients in whom the appearance of mycosis fungoides followed the B-cell malignancy, three had been treated with multiagent chemotherapy. Two patients who presented with early-stage mycosis fungoides (IA) as the first lymphoma developed mycosis fungoides tumours after becoming immunosuppressed. In two patients infiltrates composed of both malignant T- and B-cell populations were found in a single biopsy. One showed two distinct populations of the malignant cells in the skin tumour, thus constituting a classical composite lymphoma of mycosis fungoides and chronic lymphocytic leukaemia, while in the other patient the two malignant populations of marginal B-cell lymphoma and mycosis fungoides (as evidenced by both phenotypic and genotypic findings) were intermingled.
Conclusions This case series indicates that while the coexistence of Hodgkin's lymphoma and mycosis fungoides is extremely rare, the association of mycosis fungoides and B-cell malignancies is not as rare as reflected in the literature, with non-Hodgkin's lymphoma constituting the most common associated B-cell malignancy. In this series as well as in the cases reported in the literature mycosis fungoides usually preceded the development of B-cell malignancies, which may be in accordance with previous reports of an increased risk of developing a second haematological neoplasm. The importance of a competent immune system for patients with mycosis fungoides is well demonstrated in these cases. It is suggested that for greater precision the criteria for diagnosis of composite lymphoma of the skin should include both phenotypic and genotypic features.