Detection of API2-MALT1 Fusion Transcripts in Cytologic Specimens of Patients with Pulmonary Mucosa-Associated Lymphoid Tissue Lymphoma

An Unusual Presentation of Pulmonary Mucosa-Associated Lymphoid Tissue Lymphoma as Diffuse Pulmonary Infiltrates with Spontaneous Regression

A 57-year-old woman presented with cough and dyspnea for 2 months. Computed tomography of the chest showed diffuse ground-glass opacities in both lungs. Histologic examination via thoracoscopic lung biopsy revealed atypical lymphoproliferative lesion. Her symptoms and radiologic findings of the chest improved just after lung biopsy without any treatment. Therefore, she was discharged and monitored at an outpatient clinic. Two months later, pulmonary mucosa-associated lymphoid tissue (MALT) lymphoma was confirmed by the detection of API2-MALT1 translocation in fluorescent in situ hybridization analysis. Although the lung lesions resolved spontaneously, she received chemotherapy due to bone marrow involvement in her staging workup. Pulmonary MALT lymphoma is rare. Nodular or consolidative patterns are the most frequent radiologic findings. Although the disease has an indolent growth, it rarely resolves without treatment. We report an unusual case of pulmonary MALT lymphoma with diffuse interstitial abnormalities on image and spontaneous regression on clinical course.

Mucosa-associated lymphoid tissue lymphoma: molecular pathogenesis and clinicopathological significance

Mucosa-associated lymphoid tissue (MALT) lymphoma is a low-grade tumor closely associated with chronic inflammation such as that of Helicobacter pylori gastritis, Sjogren's syndrome, and Hashimoto's thyroiditis. Tumor regression by H. pylori eradication alone is well known in gastric MALT lymphoma, but some tumors occur in the absence of pre-existing chronic inflammation. The understanding of MALT lymphoma biology has significantly improved, and recurrent cytogenetic alterations have been detected. These include the trisomies 3 and 18, and the translocations t(11;18)(q21;q21), t(1;14)(p22;q32), t(14;18)(q32;q21), and t(3;14)(p14.1;q32). At least some of these alterations result in the constitutive activation of the nuclear factor (NF)-kappaB pathway, and may exert anti-apoptotic action. Apoptosis inhibitor 2-MALT lymphoma-associated translocation 1 (API12-MALT1) fusion, resulting from t(11;18)(q21;q21), is specific to, and is the most common in, MALT lymphomas, and its clinicopathological significance has been studied extensively. The focus of the present review is on the recent progress made in elucidating MALT lymphomagenesis and its clinicopathological impact, especially in terms of the effect of API2-MALT1 fusion on this unique tumor.