No abstract

Inflammatory myofibroblastic tumor (IMT) is a neoplasm which typically occurs in children. The genetic landscape of this tumor is incompletely understood and therapeutic options are limited. While 50% of IMTs harbor ALK rearrangements, no therapeutic targets have been identified in ALK negative tumors. We report for the first time that IMTs harbor other actionable targets, including ROS1 and PDGFRβ fusions. We detail the case of an 8 year old boy with treatment-refractory ALK negative IMT. Molecular tumor profiling revealed a ROS1 fusion, and he had a dramatic response to the ROS1 inhibitor, crizotinib. This case prompted assessment of a larger series of IMTs. Next generation sequencing revealed that 85% of cases evaluated harbored kinase fusions, involving ALK, ROS1, or PDGFRβ. Our study represents the most comprehensive genetic analysis of IMTs to date and also provides rationale for routine molecular profiling of these tumors to detect therapeutically actionable kinase fusions.

Inflammatory myofibroblastic tumor (IMT) is a neoplasm of intermediate biologic potential. In this study, we report a subset of IMTs with histologic atypia and/or clinical aggressiveness that were analyzed for clinicopathologic features, outcome, and immunohistochemical expression of anaplastic lymphoma kinase (ALK) and other markers to identify potential pathologic prognostic features. Fifty-nine IMTs with classic morphology (5 cases), atypical histologic features (21 cases), local recurrence (27 cases), and/or metastasis (6 cases) were studied. Immunohistochemistry was performed for ALK1 and other markers (Mib-1, c-Myc, cyclin D1, caspase 3, Bcl-2, Mcl-1, survivin, p27, CD56, p53, MDM-2) using standard techniques. The 59 IMTs had an age at diagnosis ranging from 3 weeks to 74 years (mean 13.2 y, median 11 y, 44% in the first decade). The mean tumor size was 7.8 cm. Sites included the abdomen or pelvis in 64%, lung in 22%, head and neck in 8%, and extremities in 5%. The follow-up ranged from 3 months to 11 years, with a mean of 3.6 years and a median of 3 years. Thirty-three patients had local recurrences, including 13 with multiple local recurrences and 6 patients with both local recurrences and distant metastases. Six patients died of disease, 5 with local recurrences, and 1 with distant metastases. Histologic evolution to a more pleomorphic cellular, spindled, polygonal, or round cell morphologic pattern was observed in 7 cases. Abdominal and pelvic IMTs had a recurrence rate of 85%. Recurrent and metastatic IMTs were larger, with mean diameters of 8.7 and 11 cm, respectively. Cytoplasmic ALK reactivity was seen in 56%. ALK-negative IMTs occurred in older patients (mean age 20.1) years and had greater nuclear pleomorphism, atypia, and atypical mitoses. All 6 metastatic IMTs were ALK-negative. Nuclear expression of p53 was detected in 80% of IMTs overall, but in only 25% of the metastatic subset. There were no significant differences among the subgroups for c-Myc, cyclin D1, MDM-2, Mcl-1, Bcl-2, CD56, p27, caspase 3, or survivin expression. In conclusion, among these 59 IMTs, ALK reactivity was associated with local recurrence, but not distant metastasis, which was confined to ALK-negative lesions. Absent ALK expression was associated with a higher age overall, subtle histologic differences, and death from disease or distant metastases (in a younger subset). Other proliferative, apoptotic, and prognostic markers did not correlate well with morphology or outcome. Thus, ALK reactivity may be a favorable prognostic indicator in IMT and abdominopelvic IMTs recur more frequently.