Primary thoracic neoplasms are rare in children, whereas nonneoplastic mass lesions or cysts and metastases are more common, and there is a relative paucity of comprehensive histopathologic and molecular data.


To define the clinicopathologic spectrum of neoplastic and nonneoplastic diseases observed in resected mass lesions in the chest of pediatric patients, and to identify somatic alterations observed in primary neoplasms.


Clinicopathologic features of thoracic mass lesions (n = 385) resected from 373 patients aged ≤21 years in a 25-year period (1993–2018) were included. Primary neoplasms having sufficient material were tested by a laboratory-developed comprehensive genomic profiling assay that assesses tumor mutational burden, microsatellite instability, somatic sequence variants, gene amplifications, fusions, and specific transcript variants.


The most commonly resected space-occupying lesions were nonneoplastic mass lesions and cysts or malformations, resected in 117 (31.4%) and 58 of 373 patients (15.5%) respectively. Metastatic neoplasms were observed in 169 of 373 patients (45.3%; mean age 14.4 years, range 1–21 years); the most common was osteosarcoma (68 of 169; 40.2% of metastases). Primary lung neoplasms occurred in 24 of 373 patients (6.4%; mean age 14.5 years, range 6 months–21 years), and 16 patients had primary extrapulmonary thoracic tumors. Carcinoid tumor was the most common primary lung neoplasm (7 typical, 3 atypical). Molecular testing showed a prevalence of somatic pathogenic or likely pathogenic mutations and copy-number alterations. No fusions or splice variants were identified. Tumors were microsatellite-stable with low tumor mutational burden.


Resected pediatric thoracic mass lesions are more likely to be metastatic lesions, congenital cysts or malformations, or nonneoplastic lesions compared to primary thoracic neoplasms, which are encountered at a low frequency and tend to have relatively simple genetic profiles.

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Competing Interests

The authors have no relevant financial interest in the products or companies described in this article.

Author notes

This work was presented in its preliminary form as a poster presentation at the United States and Canadian Academy of Pathology Annual Meeting in Los Angeles, California; March 23, 2022.

Supplementary data