# A case of pulmonary mucosa-associated lymphoid tissue (MALT) lymphoma in a patient with a history of idiopathic lymphocytic interstitial pneumonia (iLIP)

## TL;DR

A rare case of MALT lymphoma developed 9 years after a diagnosis of LIP in a patient, highlighting the importance of monitoring LIP for potential malignant transformation.

## Contribution

This case report highlights the rare progression of idiopathic lymphocytic interstitial pneumonia to MALT lymphoma and emphasizes the diagnostic and treatment challenges.

## Key findings

- MALT lymphoma can develop from LIP after a long latency period.
- Diagnosis of pulmonary lymphoma requires biopsy techniques due to overlapping clinical and imaging features.
- Surgery is a standard treatment for primary pulmonary lymphoma, but observation can also be effective.

## Abstract

Pulmonary mucosa-associated lymphoid tissue (MALT) lymphoma and idiopathic lymphocytic interstitial pneumonia (iLIP) are rare pulmonary diseases. MALT lymphoma is an extranodal marginal zone lymphoma (EMZL), whereas LIP is a benign lymphoproliferative disorder characterized by lymphocytic infiltration of the lungs. LIP should be closely monitored, as it has the potential to undergo malignant transformation into MALT lymphoma.

A 45-year-old woman was diagnosed with LIP and followed up for 9 years before being referred to our hospital due to an enlarging shadow on chest radiographs. The volume of the sample collected via bronchoscopy was too small to make a diagnosis, so the patient underwent surgery. The pathology results revealed diffuse proliferation of medium-sized lymphocytes filling the alveolar spaces, leading to a diagnosis of MALT lymphoma. After a thorough examination, no other lesions were found, confirming the diagnosis of EMZL of the lung, a primary pulmonary lymphoma (PPL). No postoperative treatment was administered after surgery; however, 2 years later, recurrence was detected in the stomach, and the patient underwent chemotherapy. Complete remission was achieved through chemotherapy, and the patient has been recurrence-free for 3 years since her treatment.

We report a rare case of MALT lymphoma that developed 9 years after the diagnosis of LIP. Since LIP can undergo malignant transformation into EMZL, it is important to be aware of this possibility. Differentiating between the two diseases onthe basis ofclinical and imaging findings is challenging, so biopsytechniques, such as transbronchial biopsy, CT-guided needle aspiration biopsy, and surgical resection, are essential. While surgery is the standard treatment for primary pulmonary lymphoma, observation is a viable option, as it provides results comparable to those of other treatment approaches.

The online version contains supplementary material available at 10.1186/s44215-025-00208-3.