Romano, Ryan C.

Abstract: Primary cutaneous sweat gland carcinomas (SGCs) are rare tumors that commonly involve axillae, have a high local recurrence rate, and rarely show sarcomatoid transformation. A 68-year-old man presented with rapid enlargement of a previously stable, asymptomatic pea-sized nodule in the left axilla. Initial excision (with positive surgical margins) at another institution showed characteristic histologic features of a high-grade osteosarcoma and molecular analysis using a 92-gene real-time quantitative reverse transcription–polymerase chain reaction assay confirmed a diagnosis of osteosarcoma with 96% certainty. Notably, the molecular assay demonstrated consistently high relative expression of pannexin 3 (PANX3), a gene involved in normal osteoblast differentiation which, when highly expressed, strongly predicts osteosarcoma per the assay's algorithm. However, on further histologic review, the tumor also contained focal cystic areas, nests, and ducts composed of malignant epithelial cells reminiscent of SGC; these areas directly transitioned into the osteosarcomatous component and were strongly positive for pancytokeratin, CK7, and p63. Within 2 weeks, the lesion recurred and grew rapidly, prompting complete resection, histologic sections of which showed high-grade osteosarcoma without residual epithelial elements. This is the fifth report, to our knowledge, of osteosarcomatous transformation in a SGC, and the only report to date including molecular data. This case demonstrates that osteosarcoma arising from a SGC has a similar molecular profile to de novo primary osteosarcoma of bone. It also emphasizes the importance of histopathologic findings as the established diagnostic gold standard and the need to interpret molecular results within the clinical context.

Background. Malignant melanoma of the nail apparatus is exceedingly rare. Increasingly, genetic studies have been employed to aid in distinguishing between malignant melanoma and benign melanocytic nevi. Methods. Archived nail apparatus melanomas were analyzed by fluorescence in situ hybridization (FISH) using probes targeting the genes at 6p25 (RREB1), 11q13 (CCND1), 8q24.1 (MYC), 6q23 (MYB), 9p21 (CDKN2A) and the centromeres of chromosomes 8 (D8Z2) and 6 (D6Z1). The results were correlated with clinical and demographic information. Results. Mean patient age was 57.8 years (range 23-92 years). In all, 5 of 7 (71%) cases involved the upper extremity digits. RREB1 gain was seen in all cases. CCND1 gain was seen in 6 of 7 (86%) cases, 3 of which were amplified. MYB loss and MYC gain were both seen in 5 of 7 (71%) cases. Homozygous loss of CDKN2A was not observed in any case. Two of 7 (28.6%) patients had lymph node metastasis and died of widely metastatic disease. These 2 patients harbored the most genetic aberrations: gains of RREB1, CCND1, and MYC, and MYB loss. Both benign melanocytic nevi controls showed normal FISH results. Conclusions. RREB1 and CCND1 gains are common in nail apparatus melanoma as in most melanomas, and an increased number of genetic aberrations may be associated with a poorer prognosis, though the limited number of cases precludes definitive correlation. FISH appears to be a useful adjunct in the diagnosis of nail apparatus melanomas and improves diagnostic confidence even in the setting of unambiguous histomorphology.

AbstractPhakomatous choristoma (PC) is a rare benign congenital lesion of lenticular anlage. It presents in young patients as a firm subcutaneous mass in the medial eyelid or orbit and may raise clinical concern for neoplasms such as rhabdomyosarcoma, but its histopathology is distinct, consisting of dense collagenous stroma and eosinophilic cuboidal epithelial cells forming nests, tubules, cords, or pseudoglands. We present a case of PC in a 10‐week‐old boy to illustrate the unique clinical, histopathologic, and immunophenotypic features of this condition and to reaffirm that familiarity with this rare entity aids accurate diagnosis.

Kayexalate (sodium polystyrene sulfonate), a cation exchange resin often used to treat hyperkalemia, is known to produce gastrointestinal complications in a minority of patients. These complications range from mild gastrointestinal bleeding to perforation with acute abdomen. The typical histopathologic findings include mucosal ulceration, necrosis, and the presence of polygonal basophilic refractile crystals with a “fish scale” appearance. We present a unique case of Kayexalate crystals embedded in a perihepatic inflammatory pseudotumor, developing adjacent to a colostomy site in a 62-year-old woman following Kayexalate treatment. Microscopically, the lesion demonstrated a myofibroblastic proliferation rich in histiocytes and inflammation (lymphocytes, plasma cells, and eosinophils) as well as the presence of scattered typical Kayexalate crystals. This is the first report of extraintestinal Kayexalate identification in association with an inflammatory pseudotumor.