What happened, in summary

A 69-year-old man with systemic sclerosis, interstitial lung disease, and a long smoking history was evaluated for a worsening abnormality in the right upper lung. Initial testing suggested a difficult mycobacterial infection, later identified as Mycobacterium malmoense. Despite medication, part of the lung lesion continued to enlarge.

Because the abnormality remained localized, he underwent a right upper-lung segmentectomy. The resected specimen contained both the infectious granulomatous changes and a separate 1-cm well-differentiated squamous cell carcinoma. The cancer had not been identified in the earlier bronchoalveolar sample. Surgical margins were negative, indicating complete removal of the tumor.

After surgery, he was followed without further antibiotic treatment. At 9 months, imaging showed no recurrence of the lung cancer, no recurrence of the Mycobacterium malmoense infection, and no new lung abnormalities. His case shows how infection and lung cancer can coexist in the same region and complicate interpretation of changing lung findings.