Inflammatory myofibroblastic tumors of the lung carrying a chimeric A2M–ALK gene: report of two infantile cases and review of the differential diagnosis of infantile pulmonary lesions

Publication date: Available online 11 July 2017
Source:Human Pathology
Author(s): Mio Tanaka, Kenichi Kohashi, Kei Kushitani, Misa Yoshida, Sho Kurihara, Masumi Kawashima, Yuka Ueda, Ryota Souzaki, Yoshiaki Kinoshita, Yoshinao Oda, Yukio Takeshima, Eiso Hiyama, Tomoaki Taguchi, Yukichi Tanaka
We report two infantile cases of pulmonary tumor carrying a chimeric A2M–ALK gene. A2M–ALK is a newly identified anaplastic lymphoma kinase (ALK)-related chimeric gene from a tumor diagnosed as fetal lung interstitial tumor (FLIT). FLIT is a recently recognized infantile pulmonary lesion defined as a mass-like lesion that morphologically resembles the fetal lung. Grossly, FLIT characteristically appears as a well-circumscribed spongy mass, whereas the tumors in these patients were solid and firm. Histologically, the tumors showed intrapulmonary lesions composed of densely proliferating polygonal or spindle-shaped mesenchymal cells with diffuse and dense infiltrations of inflammatory cells, forming microcystic or micropapillary structures lined by TTF1-positive pneumocytes, favoring IMT rather than FLIT. The proliferating cells were immunoreactive for ALK, and A2M–ALK was identified in both tumors with reverse transcription (RT)–PCR. The dense infiltration of inflammatory cells, immunoreactivity for ALK, and the identification of an ALK-related chimeric gene suggested a diagnosis of inflammatory myofibroblastic tumor. Histologically, most reported FLIT show sparse inflammatory infiltrates and a relatively low density of interstitial cells in the septa, although prominent infiltration of inflammatory cells and high cellularity of interstitial cells are seen in some FLITs. The present cases suggest that ALK rearrangements, including the chimeric A2M–ALK gene, may be present in these infantile pulmonary lesions, especially those with inflammatory cell infiltration. We propose that these infantile pulmonary lesions containing a chimeric A2M–ALK gene, be categorized as a specific type of IMT that develops exclusively in neonates and infants.



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