Pulmonary carcinoid tumorlet without underlying lung disease: analysis of its relationship to fibrosis

Pulmonary carcinoid tumorlet is a rare pathology and appears to be always associated with other lesions such as bronchiectasis and fibrosis. While the cause-effect relationship between tumorlet and the accompanying pathological changes in the surrounding mesenchymal tissue remains to be defined, it has been postulated that pulmonary fibrosis may be the primary pathology underlying the development of tumorlet. In this paper, we present a case where a tumor (<0.5 cm) was detected in the right upper lobe of a 71-year old woman. Cells of the tumor displayed markers characterizing for their neuroendocrine origin. No histological evidence for inflammation, interstitial fibrosis and remodeling of vascular structure was observed. However, immunohistochemistry assay demonstrated a strong production of the profibrotic factors VEGF and TGF-β1 by tumor cells. These findings suggest that carcinoid tumorlet can be an isolated lesion and pulmonary fibrosis that “often co-exists” with tumorlet may be secondary to the paracrine effects of fibrotic growth factors produced by tumorlet.