# Case Report: A rare case of pulmonary actinomycosis and concomitant small cell lung cancer

## TL;DR

A rare case of both a lung infection called actinomycosis and small cell lung cancer is reported, highlighting the need for careful diagnosis.

## Contribution

This case report highlights the rare coexistence of pulmonary actinomycosis and small cell lung cancer.

## Key findings

- Pulmonary actinomycosis was confirmed in the left lung mass and resolved with penicillin treatment.
- The right lung nodule was diagnosed as small cell lung cancer after thorough evaluation.
- The coexistence of these two conditions is extremely rare and emphasizes the need for accurate diagnosis.

## Abstract

Pulmonary actinomycosis is a rare chronic granulomatous infection with non-specific clinical and imaging manifestations, often misdiagnosed as lung cancer. We present the case of an elderly male smoker with two pulmonary space-occupying lesions on the left and right sides, respectively, both showing hypermetabolism on positron emission tomography-computed tomography (PET/CT). The CT-guided lung biopsy of the left mass confirmed pulmonary actinomycosis. After treatment with penicillin for 1 month, the left lung mass got resolved significantly, while the right lung nodule increased during this period. Subsequently, the right nodule was diagnosed as small cell lung cancer via the endoscopic ultrasonography combined with LungPro navigation-guided transbronchoscopic lung biopsy and underwent thoracoscopic resection. The coexistence of pulmonary actinomycosis and lung cancer is extremely rare. This case underscores the importance of thorough diagnostic evaluation and careful differentiation between infectious and neoplastic pulmonary conditions to ensure appropriate management.