Anorectal Malignant Melanoma

Primary Small Cell Malignant Melanoma of the Rectum: Case Report of a Very Rare Tumor

Rectal/anorectal malignant melanomas are highly aggressive tumors with a poor prognosis and low 5-year survival rate. They are also very rare. Of the well-known histological variants of malignant melanoma, the small cell subtype is also very uncommon; consequently, small cell anorectal malignant melanoma is an exceedingly rare occurrence. In this article, the authors provide a detailed clinicopathological description of small cell malignant melanoma of the rectum, documenting clinical, histological, immunohistochemical, and ultrastructural features, to add to the sparse references on this tumor in the literature. The patient was a 53-year-old woman with a mass 2 cm from the anus, which was surgically removed. In histological sections, the tumor was a small cell malignant melanoma, with a tumor cell diameter of 7.6+/-1.0 microm, and a range of 5.5-10.7 microm (N = 100). Tumor cells were positive for S-100 protein and HMB-45 and contained sparse but unambiguous type II melanosomes. This article is one of the few detailed clinicopathological documentations of a small cell malignant melanoma of the rectum (anorectum) and the first to have the diagnosis confirmed ultrastructurally by the identification of melanosomes. The present case adds to the 3 mainly or entirely small cell anorectal malignant melanomas described in the literature. There are also at least 12 other cases with less well-defined numbers of small tumor cells or with small cells admixed with other cell morphologies. Documentation of these unusual morphological variants is important for identifying any distinctive outcome they might exhibit compared with conventional malignant melanoma.

Polypoid PEComa in the rectum of a 15-year-old girl: case report and review of PEComa in the gastrointestinal tract

PEComa of the gastrointestinal tract, composed of perivascular epithelioid cells with myomelanocytic differentiation, is rare with previous literature limited to 16 case reports. There is a marked female preponderance and approximately one-third of the cases occur in the pediatric age group. We report PEComa with lymph node involvement occurring in the rectum of a 15-year-old girl, treated by surgical resection and adjuvant chemotherapy. The patient is well at 9 months follow-up with neither radiologic nor endoscopic evidence of recurrence. We review the differential diagnosis of intestinal PEComa, which includes malignant melanoma, epithelioid gastrointestinal stromal tumors, clear cell sarcoma of soft parts, alveolar soft part sarcoma, leiomyosarcoma with HMB45 expression, and paraganglioma. Immunohistochemistry can rule out many of these morphologically similar tumors but differentiation from clear cell sarcoma may require reverse transcription-polymerase chain reaction. We discuss the determination of pathologic features indicative of malignancy in PEComa, which is complicated in the gastrointestinal tract due to the small number of cases, variability of pathologic features reported, and inconsistent reporting of outcome. All 4 tumors reporting early recurrence or progression were greater than 5 cm in size and had areas of coagulative tumor necrosis. In addition, high nuclear grade and lymphovascular invasion were seen in 2 of these 4 cases. We propose that a minimum dataset for gastrointestinal PEComa should include these features along with mitotic count, infiltrative border, and tumor stage analogous to that used in colorectal carcinoma.

Analysis of c-KIT expression and KIT gene mutation in human mucosal melanomas

Recent data suggested an increased frequency of KIT aberrations in mucosal melanomas, whereas c-KIT in most types of cutaneous melanomas does not appear to be of pathogenetic importance. However, studies investigating the status of the KIT gene in larger, well-characterised groups of patients with mucosal melanomas are lacking. We analysed 44 archival specimens of 39 well-characterised patients with mucosal melanomas of different locations. c-KIT protein expression was determined by immunhistochemistry, KIT gene mutations were analysed by PCR amplification and DNA sequencing of exons 9, 11, 13, 17 and 18. c-KIT protein expression could be shown in 40 out of 44 (91%) tumours in at least 10% of tumour cells. DNA sequence analysis of the KIT was successfully performed in 37 patients. In 6 out of 37 patients (16%) KIT mutations were found, five in exon 11 and one in exon 18. The presence of mutations in exon 11 correlated with a significant stronger immunohistochemical expression of c-KIT protein (P=0.015). Among the six patients with mutations, in two patients the primary tumour was located in the head/neck region, in three patients in the genitourinary tract and in one patient in the anal/rectal area. In conclusion, KIT mutations can be found in a subset of patients with mucosal melanomas irrespective of the location of the primary tumour. Our data encourage therapeutic attempts with tyrosine kinase inhibitors blocking c-KIT in these patients.

Gastrointestinal melanoma or clear cell sarcoma? Molecular evaluation of 7 cases previously diagnosed as malignant melanoma

Clear cell sarcoma (CCS) is a rare tumor classically associated with the tendons and aponeuroses of distal extremities of young adults. CCS and malignant melanoma (MM) share immunohistochemical profiles and ultrastructural features, but classic CCS has characteristic morphology with low mitotic activity and minimal pleomorphism. Occasional cases show pleomorphism, high mitotic index, and/or melanin pigmentation, making CCS indistinguishable from MM based on morphology. However, CCS is genetically distinct owing to its consistent association with a t(12;22)(q13;q12) chromosomal translocation, leading to the formation of the EWS/ATF1 fusion transcript. This translocation has never been documented in cutaneous melanoma, and thus is regarded as specific for CCS. Recent evidence suggests that primary "malignant melanomas" in unusual anatomic sites, most notably the gastrointestinal (GI) tract, may be CCS. This is supported by 11 cases of primary GI CCS with the t(12;22) translocation. We used reverse-transcription polymerase chain reaction and fluorescence in situ hybridization to examine whether a proportion of cases diagnosed as MM of the GI tract in patients without a history of cutaneous MM actually represent primary GI CCS. In total, we examined 7 cases: Four with no prior history of MM, 2 with histories of cutaneous MM, and 1 with an anal MM. All 4 cases for which there was no history of cutaneous/mucosal MM harbored the EWS/ATF1 fusion transcript. We report the largest series of GI CCS and have shown that molecular studies may be warranted in cases that otherwise seem to represent MM of unusual primary locations.

[Anal and anal margin tumors]

Tumors of the anal canal and anal margin are rare. They may raise specific problems for the pathologist. Benign tumors mainly consist of condylomas, cloacogenic polyps and fibro-epithelial polyps. Cancers are infrequent and consisted of well-differentiated squamous cell carcinoma, or poorly differentiated basaloid squamous cell carcinoma. The other malignant tumors are very rare.

Primary malignant melanoma of the transverse colon: report of a case and review of the literature

Gastrointestinal involvement by malignant melanoma is predominantly a metastatic phenomenon. Although primary malignant melanoma of the gastrointestinal tract has been documented in the esophagus, stomach, small bowel, and anorectum, the incidence of primary melanoma of the colon is rare and remains controversial in most cases. We present a case of solitary malignant melanoma of the transverse colon occurring in a 64-year-old African American male patient. Complete dermatologic and ophthalmologic examinations revealed no evidence of a cutaneous or an ocular primary lesion. Microscopic examination of the resection specimen revealed malignant melanoma, which was confirmed by immunohistochemical positivity for S100 and melan-A. We believe that this tumor represents a primary colonic malignant melanoma.

L576P KIT mutation in anal melanomas correlates with KIT protein expression and is sensitive to specific kinase inhibition

Activating mutations in either BRAF or NRAS are seen in a significant number of malignant melanomas, but their incidence appears to be dependent to ultraviolet light exposure. Thus, BRAF mutations have the highest incidence in non-chronic sun damaged (CSD), and are uncommon in acral, mucosal and CSD melanomas. More recently, activating KIT mutations have been described in rare cases of metastatic melanoma, without further reference to their clinical phenotypes. This finding is intriguing since KIT expression is downregulated in most melanomas progressing to more aggressive lesions. In this study, we investigated a group of anal melanomas for the presence of BRAF, NRAS, KIT and PDGFRA mutations. A heterozygous KIT exon 11 L576P substitution was identified in 3 of 20 cases tested. The 3 KIT mutation-carrying tumors were strongly immunopositive for KIT protein. No KIT mutations were identified in tumors with less than 4+ KIT immunostaining. NRAS mutation was identified in one tumor. No BRAF or PDGFRA mutations were identified in either KIT positive or negative anal melanomas. In vitro drug testing of stable transformant Ba/F3 KIT(L576P) mutant cells showed sensitivity for dasatinib (previously known as BMS-354825), a dual SRC/ABL kinase inhibitor, and imatinib. However, compared to an imatinib-sensitive KIT mutant, dasatinib was potent at lower doses than imatinib in the KIT(L576P) mutant. These results suggest that a subset of anal melanomas show activating KIT mutations, which are susceptible for therapy with specific kinase inhibitors.

Gastrointestinal stromal tumors: diagnostic challenges and practical approach to differential diagnosis

Over the last decade, gastrointestinal stromal tumors (GISTs) have evolved from histogenetically obscure gastrointestinal mesenchymal tumors to well-defined tumors with distinctive clinical, morphologic, ultrastructural, histogenetic, and molecular characteristics, for which targeted therapy is available. This is largely attributable to the discovery of CD117 overexpression and activating mutations in c-kit or platelet-derived growth factor alpha genes in most of GISTs. The availability of specific diagnostic tests and targeted therapy for GISTs has led to an increased awareness of these tumors. At the same time, the list of potential GIST mimics has lengthened considerably and it has become increasingly important that GISTs be distinguished from their mimics because correct diagnosis has implications for both treatment and prognosis. The purpose of this review is to provide an update of the expanding differential diagnosis of GISTS, to draw attention to unusual GIST variants, to provide a practical approach the differential diagnosis of GISTs and to highlight some of the challenges faced by pathologists in resolving this differential diagnosis.