Primary Mediastinal (Thymic) Large B-Cell Lymphoma: Diagnostics of Extramediastinal Lesions and Treatment Opportunities

Background. Current diagnostic methods and the introduction of molecular investigations into clinical practice allow to improve the understanding of classical primary mediastinal (thymic) large B-cell lymphoma (PMBCL). Aim. To investigate clinical characteristics of PMBCL patients with extramediastinal lesions. Materials & Methods. The study was performed from 2007 to 2017 in the National Medical Hematology Research Center and included 157 PMBCL patients. The data of 16 (10.2 %; 4 men and 12 women) patients with extramediastinal lesions were analyzed; the median age was 27 years (range 23–69). Results. The extramediastinal lesions were found in pancreas (6; 37.5 %), kidneys (5; 31.2 %), ovaries (3; 18.7 %), liver (3; 18.7 %), bone marrow (3; 18.7 %), and breasts (2; 12 %); the lesions in stomach, bones, soft tissues, spleen, adrenals, and small pelvis were observed each in a single case. In 15 of 16 cases extramediastinal lesions were accompanied by involvement of superior mediastinum, and only 1 patient had an isolated lesion in thoracic soft tissues without mediastinal involvement. The samples of 8 out of 16 patients were analyzed using PCR. In all samples overexpression of 2 or more genes (JAK2, TRAF1, MAL, PDL1, PDL2) was determined which allowed to confirm, and in some cases to revise the diagnosis of PMBCL. Overall 5-year survival (93 %) of patients with classical PMBCL with thoracic involvement was similar to the cohort with extramediastinal lesions. All unfavourable events (progression/relapse) were identified at an early stage, i.e. within a year after the completion of therapy. Conclusion. PMBCL patients can have not only superior mediastinum involvement, but extramediastinal lesions as well, including bone marrow. The spreading of the disease beyond superior mediastinum should be differentiated from diffuse large B-cell lymphoma using standard evaluation methods, and molecular analysis in some cases.