Figure 1. Histologic, Immunohistochemical, and Molecular Analyses of IMT Samples from Patient 1.

A sample of the inflammatory myofibroblastic tumor (IMT) obtained on biopsy shows epithelioid cells containing vesicular nuclei, prominent nucleoli, and amphophilic cytoplasm embedded in a myxoid stroma containing prominent neutrophils (Panel A, hematoxylin and eosin). Immunohistochemical analysis for ALK shows positive staining in tumor cells, with a nuclear membrane pattern (Panel B). Dual-color fluorescence in situ hybridization (FISH) shows rearrangement of centromeric (green) and telomeric (orange) probes flanking the ALK locus at 2p23 (Panel C). Gel electrophoresis of polymerase-chain-reaction (PCR) products after reverse-transcriptase PCR (RT-PCR) is shown for primers directed at known ALK translocation partners in IMT, including CARS, CLTC, RANBP2, ATIC, SEC31L1 (which generates both long-form [L] and short-form [S] fusion transcripts), TPM3, and TPM4⁴,⁹ (Panel D). Only RANBP2-ALK primers produce an amplification product in the presence of (but not in the absence of) reverse transcriptase. Sequencing of the PCR product confirmed that RANBP2 exon 18 is fused in frame with ALK exon 20 (Panel E). Sections from progressing tumor masses in the liver (Panel F) and perirectal region (Panel G), which were resected after approximately 8 months of crizotinib administration, show histologic heterogeneity, with cellular areas similar in appearance to the initial biopsy sample but also revealing extensive areas suggestive of a treatment effect, with foci of tumor-cell necrosis in the liver sample and marked stromal hyalinization in the perirectal sample (hematoxylin and eosin in Panels F and G). Methods for immunostaining, FISH, and RT-PCR are described in the Supplementary Appendix, available with the full text of this article at NEJM.org.