Jason L. Hornick

Inflammatory myofibroblastic tumor: comparison of clinicopathologic, histologic, and immunohistochemical features including ALK expression in atypical and aggressive cases.

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.

Crizotinib in ALK-rearranged inflammatory myofibroblastic tumor.

Inflammatory myofibroblastic tumor (IMT) is a distinctive mesenchymal neoplasm characterized by a spindle-cell proliferation with an inflammatory infiltrate. Approximately half of IMTs carry rearrangements of the anaplastic lymphoma kinase (ALK) locus on chromosome 2p23, causing aberrant ALK expression. We report a sustained partial response to the ALK inhibitor crizotinib (PF-02341066, Pfizer) in a patient with ALK-translocated IMT, as compared with no observed activity in another patient without the ALK translocation. These results support the dependence of ALK-rearranged tumors on ALK-mediated signaling and suggest a therapeutic strategy for genomically identified patients with the aggressive form of this soft-tissue tumor. (Funded by Pfizer and others; ClinicalTrials.gov number, NCT00585195.).

KIT-negative gastrointestinal stromal tumors: Proof of concept and therapeutic implications

The diagnosis of gastrointestinal stromal tumor (GIST) is currently based on morphologic features and immunohistochemical demonstration of KIT (CD117). However, some tumors (in our estimation approximately 4%) have clinicopathologic features of GIST but do not express KIT. To determine if these lesions are truly GISTs, we evaluated 25 tumors with clinical and histologic features typical of GIST, but with negative KIT immunohistochemistry, for KIT and PDGFRA mutations using DNA extracted from paraffin-embedded tissue. Most tumors originated in the stomach (N = 14) or omentum/mesentery (N = 5). The neoplasms were composed of epithelioid cells (13 cases), admixed epithelioid and spindle cells (8 cases), or spindle cells (4 cases). Absence of KIT expression was confirmed by immunoblotting in 5 cases. Tumor karyotypes performed in 4 cases were noncomplex with monosomy 14 or 14q deletion, typical of GIST. Mutational analysis revealed PDGFRA and KIT mutations in 18 and 4 tumors, respectively, whereas 3 tumors did not have apparent KIT or PDGFRA mutations. The PDGFRA mutations primarily involved exon 18 (N = 15) and included 11 tumors with missense mutation in codon 842 (PDGFRA D842V or D842Y). In conclusion, a small subset of GISTs with otherwise typical clinicopathologic and cytogenetic features do not express detectable KIT protein. When compared with KIT-positive GISTs, these KIT-negative GISTs are more likely to have epithelioid cell morphology, contain PDGFRA oncogenic mutations, and arise in the omentum/peritoneal surface. Notably, some KIT-negative GISTs contain imatinib-sensitive KIT or PDGFRA mutations; therefore, patients with KIT-negative GISTs should not, a priori, be denied imatinib therapy.

Defects in succinate dehydrogenase in gastrointestinal stromal tumors lacking KIT and PDGFRA mutations

Carney-Stratakis syndrome, an inherited condition predisposing affected individuals to gastrointestinal stromal tumor (GIST) and paraganglioma, is caused by germline mutations in succinate dehydrogenase (SDH) subunits B, C, or D, leading to dysfunction of complex II of the electron transport chain. We evaluated the role of defective cellular respiration in sporadic GIST lacking mutations in KIT or PDGFRA (WT). Thirty-four patients with WT GIST without a personal or family history of paraganglioma were tested for SDH germline mutations. WT GISTs lacking demonstrable SDH genetic inactivation were evaluated for SDHB expression by immunohistochemistry and Western blotting and for complex II activity. For comparison, SDHB expression was also determined in KIT mutant and neurofibromatosis-1–associated GIST, and complex II activity was also measured in SDH-deficient paraganglioma and KIT mutant GIST; 4 of 34 patients (12%) with WT GIST without a personal or family history of paraganglioma had germline mutations in SDHB or SDHC. WT GISTs lacking somatic mutations or deletions in SDH subunits had either complete loss of or substantial reduction in SDHB protein expression, whereas most KIT mutant GISTs had strong SDHB expression. Complex II activity was substantially decreased in WT GISTs. WT GISTs, particularly those in younger patients, have defects in SDH mitochondrial complex II, and in a subset of these patients, GIST seems to arise from germline-inactivating SDH mutations. Testing for germline mutations in SDH is recommended in patients with WT GIST. These findings highlight a potential central role of SDH dysregulation in WT GIST oncogenesis.

Inflammatory myofibroblastic tumours: where are we now?

Inflammatory pseudotumour is a generic term applied to a variety of neoplastic and non-neoplastic entities that share a common histological appearance, namely a cytologically bland spindle cell proliferation with a prominent, usually chronic inflammatory infiltrate. Over the last two decades, inflammatory myofibroblastic tumour (IMT) has emerged from within the broad category of inflammatory pseudotumour, with distinctive clinical, pathological and molecular features. IMT shows a predilection for the visceral soft tissues of children and adolescents and has a tendency for local recurrence, but only a small risk of distant metastasis. Characteristic histological patterns include the fasciitis-like, compact spindle cell and hypocellular fibrous patterns, which are often seen in combination within the same tumour. Chromosomal translocations leading to activation of the ALK tyrosine kinase can be detected in approximately 50% of IMTs, particularly those arising in young patients. This review will examine the clinical, pathological, and molecular genetic features of IMT and discuss an approach to diagnosis and differential diagnosis.

A Novel, Highly Sensitive Antibody Allows for the Routine Detection of ALK-Rearranged Lung Adenocarcinomas by Standard Immunohistochemistry

Purpose: Approximately 5% of lung adenocarcinomas harbor an EML4-ALK gene fusion and define a unique tumor group that may be responsive to targeted therapy. However ALK-rearranged lung adenocarcinomas are difficult to detect by either standard fluorescence in situ hybridization or immunohistochemistry (IHC) assays. In the present study, we used novel antibodies to compare ALK protein expression in genetically defined lung cancers and anaplastic large cell lymphomas. Experimental Design: We analyzed 174 tumors with one standard and two novel monoclonal antibodies recognizing the ALK protein. Immunostained tissue sections were assessed for the level of tumor-specific ALK expression by objective quantitative image analysis and independently by three pathologists. Results: ALK protein is invariably and exclusively expressed in ALK-rearranged lung adenocarcinomas but at much lower levels than in the prototypic ALK-rearranged tumor, anaplastic large cell lymphoma, and as a result, is often not detected by conventional IHC. We further validate a novel IHC that shows excellent sensitivity and specificity (100% and 99%, respectively) for the detection of ALK-rearranged lung adenocarcinomas in biopsy specimens, with excellent interobserver agreement between pathologists (κ statistic, 0.94). Conclusions: Low levels of ALK protein expression is a characteristic feature of ALK-rearranged lung adenocarcinomas. However, a novel, highly sensitive IHC assay reliably detects lung adenocarcinomas with ALK rearrangements and obviates the need for fluorescence in situ hybridization analysis for the majority of cases, and therefore could be routinely applicable in clinical practice to detect lung cancers that may be responsive to ALK inhibitors. Clin Cancer Res; 16(5); 1561–71

Loss of INI1 expression is characteristic of both conventional and proximal-type epithelioid sarcoma.

INI1 (hSNF5/SMARCB1), a member of the SWI/SNF chromatin remodeling complex located on chromosome 22q11.2, is deleted or/or mutated in strictly defined malignant rhabdoid tumors (MRT) of infancy. Recent studies suggest that some epithelioid sarcomas (ES) also show inactivation of INI1. However, very few cases of ES have been studied, and INI1 expression in other epithelioid malignant neoplasms has not been examined systematically. The purpose of this study was to evaluate the immunohistochemical expression of INI1 in ES compared with histologic mimics. We evaluated 350 tumors: 136 ES, including 64 conventional (“distal”) ES, 64 proximal-type ES, and 8 with hybrid features of conventional and proximal-type ES; 54 metastatic carcinomas (22 from lung, 6 breast, 6 stomach, 5 colorectum, 5 kidney, 5 prostate, 5 pancreas); 12 metastatic testicular embryonal carcinomas; 20 metastatic melanomas; 20 epithelioid mesotheliomas; 20 epithelioid angiosarcomas; 10 epithelioid hemangioendotheliomas; 24 epithelioid malignant peripheral nerve sheath tumors (MPNST); 22 myoepithelial carcinomas of soft tissue; 7 anaplastic large cell lymphomas; 5 histiocytic sarcomas; and 10 control MRT of infancy (4 brain, 3 liver, 2 soft tissue, 1 kidney). Immunohistochemistry was performed following pressure cooker heat-induced epitope retrieval using monoclonal antibody BAF47 (BD Biosciences). In total, 127 of 136 (93%) ES cases showed complete absence of INI1 expression, including 58 (91%) conventional ES, 61 (95%) proximal-type ES, and all 8 (100%) hybrid ES. Of the non-ES cases, 12 (50%) epithelioid MPNST also showed loss of INI1, as did 2 (9%) myoepithelial carcinomas and all control MRT cases. INI1 expression was intact in all other tumor types examined. In conclusion, similar to MRT of infancy, loss of INI1 expression is characteristic of both conventional and proximal-type ES, being detected in >90% of cases. Moreover, 50% epithelioid MPNST and occasional myoepithelial carcinomas are also negative for INI1. Immunostaining for INI1 can be used to confirm the diagnosis of ES in the appropriate context. Loss of INI1 expression may also be helpful to distinguish epithelioid MPNST from metastatic melanoma in a subset of cases.

PEComa: what do we know so far?

PEComas (tumours showing perivascular epithelioid cell differentiation) are a family of related mesenchymal neoplasms that include angiomyolipoma, lymphangiomyomatosis, clear cell ‘sugar’ tumour of the lung, and a group of rare, morphologically and immunophenotypically similar lesions arising at a variety of visceral and soft tissue sites. These tumours all share a distinctive cell type, the perivascular epithelioid cell or ‘PEC’ (which has no known normal tissue counterpart). PEComas show a marked female predominance and are composed of nests and sheets of usually epithelioid but occasionally spindled cells with clear to granular eosinophilic cytoplasm and a focal association with blood vessel walls. PEComas appear to arise most commonly at visceral (especially gastrointestinal and uterine), retroperitoneal, and abdominopelvic sites, with a subset occurring in somatic soft tissue and skin. Nearly all PEComas show immunoreactivity for both melanocytic (HMB‐45 and/or melan‐A) and smooth muscle (actin and/or desmin) markers. A subset of PEComas behave in a malignant fashion. This review examines the members of the PEComa family, with an emphasis on lesions arising outside of the kidney, lung and liver, and discusses preliminary evidence for pathological features that might predict malignant behaviour.

Immunohistochemical Staining for KIT (CD117) in Soft Tissue Sarcomas Is Very Limited in Distribution

We performed immunohistochemical analysis for KIT in 365 soft tissue sarcomas. Most tumors evaluated were completely negative for KIT, including all cases of leiomyosarcoma, rhabdomyosarcoma, myxofibrosarcoma, liposarcoma, solitary fibrous tumor, synovial sarcoma, dermatofibrosarcoma protuberans, schwannoma, malignant peripheral nerve sheath tumor, clear cell sarcoma, low-grade endometrial stromal sarcoma, and follicular dendritic cell sarcoma. Tumors showing occasional immunoreactivity for KIT included extraskeletal myxoid chondrosarcoma (2/20), Ewing sarcoma/malignant primitive peripheral neuroectodermal tumor (4/20), melanotic schwannoma (3/5), metastatic melanoma (4/20), and angiosarcoma (5/20). In most cases, staining for KIT was focal. Rare tumor cells showing KIT positivity were identified in a small number of other tumors. This study demonstrates very limited expression of KIT in soft tissue tumors other than gastrointestinal stromal tumors and underscores the discriminatory value of KIT immunohistochemical analysis for differential diagnosis. As some of these findings differ markedly from previous reports, it is evident again that variations in immunohistochemical technique can lead to major discrepancies in positive staining. Since treatment eligibility for selective tyrosine kinase inhibitors such as STI571 hinges on positive immunostaining, standardization and reproducibility of meaningful results are critically important.

O6-Methylguanine DNA Methyltransferase Deficiency and Response to Temozolomide-Based Therapy in Patients with Neuroendocrine Tumors

Purpose: Recent studies suggest that temozolomide has activity in neuroendocrine tumors. Low levels of the DNA repair enzyme, O6-methylguanine DNA methyltransferase (MGMT), are associated with sensitivity to temozolomide in other tumor types. We evaluated the prevalence of MGMT deficiency in neuroendocrine tumors and correlated MGMT deficiency with treatment response to temozolomide-based regimens. Experimental Design: The prevalence of MGMT deficiency, measured by immunohistochemistry, was assessed in 97 archival neuroendocrine tumor specimens. Rates of treatment response and survival were next evaluated in a cohort of 101 consecutive neuroendocrine tumor patients who had received treatment with a temozolomide-based regimen at one of three institutions. MGMT expression was directly correlated with treatment response in 21 patients who had available tumor tissue and response data. Results: In archival specimens, MGMT deficiency was observed in 19 of 37 (51%) pancreatic neuroendocrine tumors and 0 of 60 (0%) carcinoid tumors (P < 0.0001). In the clinical cohort, 18 of 53 (34%) patients with pancreatic neuroendocrine tumors but only 1 of 44 (2%) patients with carcinoid tumors (P < 0.001) experienced a partial or complete response to temozolomide-based therapy. Among 21 patients with evaluable tumor tissue who had also received treatment with temozolomide, 4 of 5 patients with MGMT-deficient tumors (all pancreatic neuroendocrine tumors) and 0 of 16 patients with tumors showing intact MGMT expression responded to treatment (P = 0.001). Conclusions: MGMT deficiency, measured by immunohistochemistry, is more common in pancreatic neuroendocrine tumors than in carcinoid tumors as is treatment response to temozolomide-based therapy. Absence of MGMT may explain the sensitivity of some pancreatic neuroendocrine tumors to treatment.