Discovered on gastrointestinal stromal tumours 1 (DOG1) expression in non-gastrointestinal stromal tumour (non-GIST) neoplasms

DOG1 expression in neuroendocrine neoplasms: Potential applications and diagnostic pitfalls

Neuroendocrine neoplasms represent a heterogeneous group of rare tumors, more frequently arising from gastroenteropancreatic tract and lungs. At the time of diagnosis, 20% of cases are metastatic, and 10% of cases are considered as cancer of unknown primary origin. Several immunohistochemical markers are routinely used to confirm the neuroendocrine differentiation, first among all Synaptophysin and Chromogranin-A; on the other hand, different immunohistochemical markers are used to establish primary anatomical site, as TTF1, CDX2, Islet-1 and Calcitonin, but no marker is available in order to distinguish among different sites of the digestive tract. DOG1 (discovered on GIST-1) is a gene normally expressed in interstitial cells of Cajal and, in routine practice, DOG1 immunostaining is used in diagnosis of GIST (gastrointestinal stromal tumor). DOG1 expression has been described in several neoplasms other than GIST, both in mesenchymal and epithelial neoplasms. In the present study, DOG1 immunostaining has been performed in a large cohort of neuroendocrine neoplasms, including neuroendocrine tumors and neuroendocrine carcinomas, in order to evaluate frequency, intensity and pattern of expression in different anatomical site and in different tumor grade. DOG1 expression was detected in a large percentage of neuroendocrine tumors, with statistically significant association between DOG1 expression and gastrointestinal tract neuroendocrine tumors. As a consequence, DOG1 could be included in marker panel for the identification of primary site in neuroendocrine metastases of unknown primary origin; moreover, these results recommend careful evaluation of DOG1 expression in gastrointestinal neoplasms, in particular in differential diagnosis between epithelioid GIST and neuroendocrine tumors.

Carcinosarcoma, a Rare Malignant Neoplasm of the Pancreas

Carcinosarcoma of the pancreas is a rare entity with poor prognosis. Here, we report a case of pancreatic carcinosarcoma in a 68-year-old male patient who underwent a pancreatoduodenectomy for a unilocular cystic mass in the head of the pancreas. Histologically, the lesion showed a biphasic tumor with a carcinoma component and a spindle cell sarcomatous component, which were intimately intermingled. Most of the carcinoma components are well-differentiated ductal adenocarcinoma with small areas of moderately to poorly differentiated ductal adenocarcinoma. The sarcomatous component is a high-grade highly cellular spindle cell tumor with frequent mitosis and apoptosis. Immunohistochemical studies demonstrated that the carcinomatous component was positive for epithelial markers and cyclin D1, and the sarcomatous component was negative for these markers while positive for vimentin, p16, and DOG1 with patchy positivity for S100. Other markers, including SOX10, CD117, Melan A, HMB45, actin, desmin, myogenin, beta-catenin, TLE1, and p53, were negative in both components. Molecular studies demonstrated that the tumor was microsatellite stable. Whole exome next generation sequencing analysis was performed and no pathogenic alterations in the genes were identified.

Successful Perioperative and Surgical Treatment of a Rare Case of Extra-Gastrointestinal Stromal Tumor Arising in the Prostate Gland

We report a very uncommon case of a primary, non-metastatic gastrointestinal stromal tumor (GIST) arising in the prostate gland in a 60-year-old patient. The morphology and immunohistochemical profile of the disease resembled GIST of gastrointestinal origin, and the molecular driver of this malignancy was a double mutation in exons 11 and 13 of the KIT gene. The tumor was proliferating slowly, did respond to neoadjuvant therapy with the KIT-inhibiting agent imatinib and was cured by radical, retro-pubic prostatectomy followed by adjuvant imatinib treatment. We postulate that primary GIST tumors of the prostate can arise from prostatic interstitial cells, which are the pacemakers of smooth muscle contractility in the gland, and possibly share a common precursor with typical GIST and the interstitial cells of Cajal in the gastrointestinal tract.

Is DOG1 Immunoreactivity Specific to Gastrointestinal Stromal Tumor?

BACKGROUND

DOG1 is a novel gene on gastrointestinal stromal tumors (GISTs) that encodes the chloride channel protein anoctamin 1, also known as discovered on GIST-1 (DOG1) protein. DOG1 antibodies are a sensitive and specific marker against GIST positive for CD117 and CD34 and negative for CD117 and CD34. DOG1 is also independent of KIT or PDGFRA mutation status and considered specific for GIST when it was first discovered in 2004.

METHODS

The previous 10 years of literature was searched for articles relating to DOG1. We critically reviewed 12 studies that showed DOG1 was positive in 250 cases of 2,360 tested non-GIST neoplasms (10.6%) at different anatomical sites using monoclonal, polyclonal, or nonspecified antibodies. Criteria for positivity varied between the studies.

RESULTS

Monoclonal and polyclonal DOG1 antibodies were reactive in various different non-GIST tumor types spanning 9 organ systems in addition to normal salivary and pancreatic tissues. The tumors included were renal oncocytoma (100%), renal cell carcinoma chromophobe type (86%), solid pseudopapillary neoplasm of the pancreas (51%), neoplastic salivary tissue (17%), synovial sarcoma (15%), leiomyoma (10%), pancreatic adenocarcinoma (7%), and leiomyosarcoma (4%).

CONCLUSIONS

By contrast to the original concept that DOG1 antibodies are specific to GIST neoplasms, the studies reviewed showed that the data suggest DOG1 positivity in select non-GIST tumors. Only in the appropriate clinical and pathological context is DOG1 positivity specific and helpful in the diagnosis of GIST.

Gastrointestinal stromal tumor with an unusual presentation as an enlarged prostate gland: a case report and review of the literature

We report a case of a 78-year-old male who presented with urinary retention, constipation and an enlarged prostate gland. A transurethral resection of the prostate (TURP) was performed. Pathologic examination revealed a hypercellular-spindled neoplasm with frequent mitoses, nuclear pleomorphism, and multifocal geographic tumoral necrosis. A pathologic diagnosis of gastrointestinal stromal tumor (GIST) was made based on morphologic and immunohistochemical findings, and was later reinforced by molecular study results. This lesion was initially thought to represent a primary prostatic GIST. To the best of our knowledge, there have been only five cases of primary prostatic GISTs. Subsequent imaging studies revealed the mass to be contiguous with the anterior rectal wall, suggesting the possibility of a rectal primary with extension to the prostate gland. The patient was treated with imatinib mesylate, and after twelve months of follow up failed to demonstrate any evidence of progression or metastatic disease. GIST should be considered in cases of prostatic tumors with a spindled or epithelioid morphology, and immunohistochemistry and possible molecular studies are recommended to aid in diagnosis and guide treatment decisions.