Pulmonary inflammatory myofibroblastic tumor coexisting with lymphangitis carcinomatosis: Mimicking metastatic papillary thyroid carcinoma with nodular fasciitis-like stroma.

Inflammatory myofibroblastic tumors (IMTs) are uncommon; intermediate grade soft tissue tumors occurring in young individuals with an uncertain behaviour. The incidence of pulmonary lymphangitis carcinomatosis (PLC) is around 6-8% of all pulmonary metastases. However, PLC due to papillary thyroid carcinoma (PTC) is very uncommon. We present a case of a 26-year-old male, who presented with a solitary left lung nodule on radiological scans. There was also a past history of thyroid surgery done two years back for PTC. Histology revealed a soft tissue tumor reminiscent of IMT. The periphery of the IMT nodule showed metastatic PTC in the form of extensive PLC. In view of this unusual histology, a diagnosis of PTC with nodular fasciitis-like stroma (PTC-NFS) was initially considered. However, molecular studies for anaplastic lymphoma kinase (ALK) gene rearrangement confirmed the diagnosis of IMT. This case highlights the unusual occurrence of tumor-to-tumor metastasis causing diagnostic challenges and also the importance of molecular testing.