Clonality and phenotyping analysis of alveolar lymphocytes is suggestive of pulmonary MALT lymphoma

Background: Mucosa-associated lymphoid tissue (MALT) lymphoma, a low-grade B-cell extranodal lymphoma, is the most frequent subset of primary pulmonary lymphoma (PPL). It often associates with connective tissue disease (CTD). We aimed to evaluate the impact of concomitant CTD on diagnostic value of flow cytometry and genetic clonality analyses for the diagnostic of MALT lymphoma.

Methods: All chest disease and pathology departments of teaching hospitals in Paris were contacted to identify patients with a histological diagnosis of PPL of the MALT subtype with or without associated CTD. We identified 44 patients in the lymphoma group; 11 had a CTD and were matched to 11 patients with CTD but without lymphoma.

Results: Results of BAL analyses of MALT-PPL showed normal cellularity (370 cells/mm(3) [range 21-2300]) but increased proportion of lymphocytes (31.5% [80-2]) of the B-cell subtype (20% [1-88]). A B-cell clone was detected in 82% of cases, and specificity of clonality was 90%. Interestingly, BAL analysis results different by presence or not of a CTD. The frequency of B lymphocyte alveolitis was significantly greater in MALT patients without than with CTD (34% vs 6.5%, p = 0.007). However, BAL results for patients with CTD did not differ between those with and without lymphoma.

Conclusion: BAL results may be highly suggestive of pulmonary MALT lymphoma. The proportion of B-cells may vary depending on the presence of an associated CTD, but clonality analyses remained informative for the diagnostic of MALT lymphoma.