A 49-year-old woman presented with fever, weight loss, night sweats, hematochezia, and acid reflux symptoms. Two large, firm cecal lesions were seen at colonoscopy, but multiple biopsies were inconclusive. The patient underwent a right hemicolectomy for a clinical diagnosis of colon cancer. Noncaseating granulomatous inflammation with background lymphocytes, plasma cells, and histiocytes exhibiting emperipolesis were identified. With these histologic features and immunoreactivity for S-100 protein and CD68, a diagnosis of Rosai-Dorfman disease was rendered. Other areas had storiform fibrosis admixed with numerous immunoglobulin G4 (IgG4)–positive plasma cells. Although a few preliminary reports have noted an increased number of IgG4-positive plasma cells in Rosai-Dorfman disease, the relationship between these 2 conditions is unclear. To our knowledge, this is the first case report of a possible association of colonic Rosai-Dorfman disease with an increased number of IgG4-positive plasma cells. Reviews of colonic Rosai-Dorfman disease and IgG4-related sclerosis are presented to heighten awareness of this rare presentation.

Although immunohistochemistry (IHC) has improved our ability to detect melanoma metastases in sentinel lymph nodes (SLN), the American Joint Committee on Cancer (AJCC) does not provide a lower threshold for determining if a SLN is positive for metastasis. Existing literature suggests that even a small aggregate or an enlarged, abnormal cell detectable by IHC can be associated with an adverse outcome. In our experience, however, some SLNs contain small solitary cells the size of neighboring lymphocytes demonstrable only by IHC. We sought to determine their clinical significance. A total of 821 patients underwent a SLN biopsy at our institution over a 12-year period. In all, 639 (77.8%) were SLN-negative, 125 (15.2%) were SLN-positive, and 57 (6.9%) had rare IHC-positive cells of undetermined clinical significance with no disease progression over a mean 59-month follow-up. Kaplan-Meier method with pair-wise comparisons revealed no significant difference in disease-specific survival and recurrence-free survival between SLN-negative and rare IHC-positive groups. There were significant differences in survival and recurrence between patients in the rare IHC-positive group and those with melanoma metastases, including those with solitary melanoma cells and those with tumor burdens ≤0.2 mm. While the lower diagnostic threshold for metastatic melanoma on IHC-stained sections needs to be studied further, our data suggest that rare IHC-positive cells lacking cytomorphologic features of overt malignancy are equivocal for melanoma and could impart a similar prognosis as patients with no evidence of SLN involvement.

WHAT IS YOUR DIAGNOSIS?Secondary syphilis, the systemic dissemination of the spirochete, Treponema pallidum, is commonly referred to as the "great mimicker" for its varied, and often protean clinical and histopathologic presentations.Classically, the clinical disease progresses through stages. The potential

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