# Mycobacterium avium complex lung infection mimics lung cancer nodules but improves after antibiotic therapy: a case series

## TL;DR

This paper reports cases where lung infections caused by Mycobacterium avium complex were mistaken for lung cancer but improved with antibiotic treatment.

## Contribution

The study highlights the use of azithromycin to distinguish infectious lung nodules from cancer, avoiding unnecessary invasive procedures.

## Key findings

- Azithromycin treatment led to improvement in lung nodule appearance on imaging.
- Non-tuberculous mycobacteria can mimic lung cancer on imaging.
- Empirical antibiotic therapy can confirm infectious etiology and prevent invasive evaluations.

## Abstract

Infection with non-tuberculous mycobacterium species commonly can present with lung nodules mimicking lung cancer on routine chest imaging, leading to unnecessary invasive procedures.

The authors report three representative cases presenting with minimal or no symptoms where an incidental probable Mycobacterium avium complex (MAC) infection was discovered, mandating evaluation for a potential malignancy. After suspecting that the nodules were likely infectious, the patients were empirically treated with azithromycin alone or in combination with other antibiotics, resulting in an improved appearance of these nodules on radiographic imaging in size, density, or both, documenting an infectious etiology, thereby preventing more invasive studies and/or surgery.

These cases represent typical examples of an increasingly common infection that can be mistaken for lung cancer, particularly in endemic areas such as the Southeast United States. Infectious etiologies, especially non-tuberculous mycobacteria, are capable of mimicking lung cancer. An empiric, 3-month course of azithromycin for suspected MAC lung infection resulting in significant nodule size reduction verifies that it is infectious and not malignant, thereby preventing invasive, potentially morbid, and expensive evaluations, including unnecessary surgery.