[Pulmonary hamartoma: a clinicopathological analysis of 316 cases]

Objective: To investigate the clinicopathological features, pathological classification, and molecular characteristics of pulmonary hamartomas. Methods: A retrospective analysis was conducted on 316 cases of pulmonary hamartomas diagnosed at Nanjing Chest Hospital, Nanjing, China from January 2015 to June 2024. Next generation sequencing (NGS) was performed on 15 cases of this study. The clinical data, histopathological features, immunophenotypes, and molecular alterations were analyzed. Relevant literature was reviewed. Results: Among the 316 patients, there were 154 males and 162 females, with an average age of 56±10 years. Among the 316 cases, 310 were intrapulmonary hamartomas and 6 were intraluminal bronchial hamartomas. Microscopically, there were complex proliferative mesenchymal components and epithelial components, presenting various combinations and hamartomatous morphologies. These hamartomas were morphologically classified into mesenchymal-type hamartomas (cartilaginous, fibrous, smooth muscle, adipose tissue, and mixed types) and epithelial-mesenchymal mixed-type hamartomas (respiratory epithelial-mesenchymal mixed and mucosal gland-mesenchymal mixed types). The cartilaginous hamartomas accounted for 72.8% (230/316) of them, and the non-cartilaginous hamartoma accounted for 27.2% (86/316). Secondary changes such as calcification, ossification, collagenization, mucin degeneration, and cystic changes were commonly present. The immunophenotype was CK7⁺/TTF1⁺ for respiratory epithelial cells, or TTF1^-/CK7⁺/p40⁺ for interstitial cells. Interstitial cells might express desmin, SMA, S-100, caldesmon, etc, while CD34⁺/CD10⁺/ER⁺ spindle-shaped interstitial cells were also commonly noted. Genetic variations were detected in 11 of the 15 cases that were subject to NGS, including HMGA2-related fusion genes, EP300 mutations, FLT1 mutations, JAK1 mutations, SETD2 and TAP2 mutations, and high-copy amplification of CDK4/PHF1/TSPAN31. The patients were followed up for 6 to 110 months without any known recurrence or metastasis. Conclusions: Pulmonary hamartomas mainly occur in the peripheral lung parenchyma, with the cartilaginous type being the most common. Their clinical pathological and molecular features of pulmonary hamartomas are characterized and the histological types are roughly ascertained in this study, with emphasis of the key points of diagnosis and differential diagnosis. Classification of pulmonary hamartomas is valuable for guiding future research. Pulmonary hamartomas overall have a good prognosis. However, those with cystic changes or intraluminal hamartomas in the bronchus may cause serious airway lesions and therefore require special attention.