Cytokeratin Expression in Gastrointestinal Stromal Tumor: A Clinicopathologic and Immunohistochemical Study of 687 Cases

NUTM1-rearranged colorectal sarcoma: a clinicopathologically and genetically distinctive malignant neoplasm with a poor prognosis

NUTM1 gene rearrangements were originally identified in NUT carcinoma. Recently, NUTM1 has been discovered to rearrange with a variety of gene partners in malignancies of diverse location and type. Only one NUTM1-rearranged tumor occurring in the colon has been reported. Herein we report five such tumors. The five tumors occurred in four females and one male, ranging from 38 to 67 years of age (median 51 years). The masses occurred in the colon (cecum, descending, sigmoid) and ileocecal valve region, measuring 2.5-20 cm in size (median 7 cm). Four patients had metastases at presentation (liver, n = 4; lymph nodes, n = 3). Histologically, the lesions arose in the submucosa, infiltrating into the mucosa and muscularis propria, and grew in fibrosarcoma-like fascicles and sheets of epithelioid or rhabdoid cells, with foci of hyalinized to vaguely osteoid-like matrix. The tumors were composed of relatively monomorphic, spindled to epithelioid cells with focal rhabdoid morphology, hyperchromatic nuclei, and small nucleoli. Mitotic activity was usually low (range 1-14/10 HPF; median 5/10 HPF); necrosis was present in two cases. Variable keratin expression and uniform nuclear NUT expression was present; KIT/DOG1 were negative and SMARCB1/SMARCA4 were retained. Next-generation sequencing identified MXD4-NUTM1 rearrangement in all cases (breakpoints: MXD4 exon 5, NUTM1 exons 2 or 3). Follow-up showed one of the four patients who presented with metastases to be dead of disease at 30 months; the other three patients were alive with metastatic disease. The final patient is disease-free, 5 months after diagnosis. NUTM1-rearranged colorectal sarcomas have characteristic morphologic, immunohistochemical, and molecular genetic features, suggesting that they represent a distinct entity within the family of NUTM1-rearranged neoplasia. A NUTM1-rearranged tumor should be considered for any difficult-to-classify submucosal spindle cell neoplasm of the gastrointestinal tract, in particular keratin-positive tumors showing an unusual combination of fibrosarcomatous, epithelioid to rhabdoid and hyalinized morphologies. Recognition of MXD4-NUTM1 rearranged sarcomas may be therapeutically important, even though best treatment is currently elusive/unknown.

Aberrant keratin expression is common in primary hepatic malignant vascular tumors: A potential diagnostic pitfall

Malignant vascular neoplasms such as epithelioid hemangioendothelioma (EHE) and angiosarcoma (AS) can arise within the liver. The aim of this study was to study the expression of keratins CK7, AE1/AE3 and OSCAR in primary hepatic EHE and AS. 9 cases of hepatic EHE and 13 cases of hepatic AS were stained with ERG, CK7, keratin AE1/AE3 and keratin OSCAR. Their expression was graded as 1+ (1-25% of tumor cells positive), 2+ (26-50%), 3+ (51-75%) or 4+ (>75%). ERG was positive in all 9 (100%) EHEs and all 13 (100%) ASs. CK7 was positive in 5/9 (56%) EHEs (2, 1+; 1, 2+; 1, 3+; 1, 4+) and 1/13 (8%) AS (2+). Keratin OSCAR was positive in 6/9 (67%) EHEs (5, 1+; 1, 2+) and 4/13 (31%) ASs (2, 1+; 1, 2+; 1, 4+). Keratin AE1/AE3 was positive in 6/9 (67%) EHEs (3, 1+; 3; 2+) and 4/13 (31%) ASs (2, 1+; 1, 2+; 1, 4+). Overall, 6/ 9 (67%) EHEs were positive for at least one keratin marker, of which 5 were positive for all 3 keratins (AE1/AE3, OSCAR and CK7) while 1 was positive only for 2 keratins (OSCAR and AE1/AE3). 4/13 (31%) of ASs were positive for both keratins OSCAR and AE1/AE3, of which 1 case was also positive for CK7. Aberrant keratin expression is common in primary hepatic EHEs (67%) and ASs (31%). Awareness of this diagnostic pitfall is important for avoiding misdiagnosis of these primary hepatic malignant vascular tumors as carcinomas.

Morphological features useful in the differential diagnosis between undifferentiated carcinoma and gastrointestinal stromal tumor

Undifferentiated (sarcomatoid) carcinomas may closely mimic gastrointestinal stromal tumors (GISTs) due to possible histological and immunohistochemical overlap between these two entities. To avoid unnecessary employment of a wide spectrum of immunohistochemical stainings and molecular genetics and thus decrease costs, finding simple morphological features to target further investigation of such neoplasms of the gastrointestinal tract would be helpful. Five cases classified as undifferentiated (sarcomatoid) carcinomas with a definite proof of the diagnosis, i. e. the presence of a differentiated carcinomatous component, were retrieved from archives of several institutions. For comparison, 84 cases of GIST mutated in KIT or PDGFRA genes served as the control group. Hematoxylin and eosin stained slides were evaluated for the presence of patterns which might discriminate between sarcomatoid carcinoma and GIST. Lymphatic invasion and entrapment of fat tissue strongly favor the diagnosis of undifferentiated carcinoma, as it was found in all or almost all cases of undifferentiated carcinoma, but in no GIST. Alternation of low- and high- grade areas, formation of angiosarcomatous-like spaces, and the presence of yolk sac-like areas were also detected in all cases of undifferentiated carcinoma, but only in 1.2%, 2.4% and 7.2% of the GISTs, respectively. Furthermore, DOG1 was negative in all cases of undifferentiated carcinoma. According to this study, the presence of the histological findings listed above should prompt extensive tumor sampling in order to find a differentiated carcinomatous component. However, due to the small number of cases of undifferentiated carcinoma available for the study, a larger multi-institutional study is warranted.

Surgical Pathology of Gastrointestinal Stromal Tumors: Practical Implications of Morphologic and Molecular Heterogeneity for Precision Medicine

Gastrointestinal stromal tumor (GIST), the most common mesenchymal neoplasm of the gastrointestinal tract, exhibits diverse histologic and clinical manifestations. With its putative origin in the gastrointestinal pacemaker cell of Cajal, GIST can arise in association with any portion of the tubular gastrointestinal tract. Morphologically, GISTs are classified as spindled or epithelioid, though each of these subtypes encompasses a broad spectrum of microscopic appearances, many of which mimic other histologic entities. Despite this morphologic ambiguity, the diagnosis of GIST is aided in many cases by immunohistochemical detection of KIT (CD117) or DOG1 expression. The natural history of GIST ranges from that of a tumor cured by surgical resection to that of a locally advanced or even widely metastatic, and ultimately fatal, disease. This clinicopathologic heterogeneity is paralleled by an underlying molecular diversity: the majority of GISTs are associated with spontaneous activating mutations in KIT, PDGFRA, or BRAF, while additional subsets are driven by genetic lesions-often inherited-of NF1 or components of the succinate dehydrogenase enzymatic complex. Specific gene mutations correlate with particular anatomic or morphologic characteristics and, in turn, with distinct clinical behaviors. Therefore, prognostication and treatment are increasingly dictated not only by morphologic clues, but also by accompanying molecular genetic features. In this review, we provide a comprehensive description of the heterogenous molecular underpinnings of GIST, including implications for the practicing pathologist with regard to morphologic identification, immunohistochemical diagnosis, and clinical management.