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Lymph node metastasis occurs in a subset of papillary microcarcinoma patients. We aimed to analyze the differences between metastatic and non-metastatic papillary microcarcinomas in order to identify a high-risk subgroup that is likely to require more aggressive treatment. 126 thyroidectomies with lymph node dissections (central ± lateral), diagnosed as papillary microcarcinoma, were reviewed. Mean age of 126 patients (F/M = 3.3) was 42 years. Mean size of the largest tumor was 7 mm. Classical was the most frequently (89%) encountered subtype. Multiple histologic subtypes co-occurred in 19%. Lymphovascular invasion was present in 16% (n = 20). 55 (44%) and 71 (56%) cases were unifocal and multifocal, respectively. 90 cases (71%) were non-encapsulated with overall infiltrative tumor borders, whereas in 36 cases (29%), the tumor had a well-defined capsule. Among those, 23 (64%) had tumor capsule invasion. 47 (37%) cases had metastasis in lymph nodes. In univariate analysis, metastasis was associated with tumor size of >5 mm (p = 0.02), tumor burden of >5 mm (p = 0.03), lymphovascular invasion (p = 0.02) and non-encapsulation (p = 0.01). No associations were found regarding sex, age, histologic subtype, lymphocytic thyroiditis, tumor capsule invasion (in capsulated tumors), laterality and multifocality (p > 0.05). In multivariate analysis, lymphovascular invasion (p = 0.01, OR = 3.97, 95% CI 1.35–11.67), tumor size >0.5 cm (p = 0.031, OR = 2.92, 95% CI 1.10–7.71) and non-encapsulation (p = 0.033, OR = 2.85, 95% CI 1.08–7.51) were independent risk factors. Size (largest tumor or sum of all foci) of >5 mm, non-encapsulation and lymphovascular invasion were independent predictors of LNM in PMs. Unifocal tumors metastasize the same as multifocal tumors, suggestive of the contribution of other factors. Patients with sporadically resected microcarcinomas should be carefully followed-up, especially those that harbor risk factors in histology. • Size (>5 mm), infiltrative borders and LVI were independent predictors of LNM in PMs. • Unifocal tumors metastasize same as multifocal tumors. • PMs without central lymph node dissection should be carefully followed-up. [ABSTRACT FROM AUTHOR]

To analyze clinicopathologic characteristics of upper gastrointestinal leiomyomas and to determine the distribution and immunohistochemical features of interstitial cells of Cajal, in order to designate whether they can cause diagnostic challenges. Twenty-four upper gastrointestinal leiomyomas (14 esophagus, 10 stomach) were retrieved. CD117, DOG-1 and muscle markers were performed. The staining was analyzed based on the distribution and percentage. Interstitial cells of Cajal were distinguished based on their positivity for both CD117 and DOG-1 immunohistochemistry, along with their morphological features. Mean age of patients was 49 years, M/F ratio was 2.4. Patients with gastric leiomyomas were significantly younger than those with esophageal leiomyomas (41.5 vs. 54.3, p = 0.012). Histologically, leiomyomas were similar to their endometrial counterpart. Immunohistochemically, all tumors had strong/diffuse positivity for muscle markers. CD117 highlighted mast cells in all cases. Three cases had prominently increased mast cells. Both CD117 and DOG-1 also highlighted interstitial cells of Cajal in 24/24 (100%) of cases. Interstitial cells of Cajal were distributed in variable proportions, from focal to homogenous. In one case, they constituted 50% of tumor cells. In 16 cases, the distribution was homogenous. Superficial leiomyomas (n = 3) had only focal CD117 and DOG-1 positivity. Upper gastrointestinal leiomyomas harbor expression of CD117 and DOG-1 in entrapped/colonized interstitial cells of Cajal, which can cause a potential pitfall in the differential diagnosis, especially in cases that show prominent immunohistochemical positivity. Evaluation of the immunohistochemistry can be exceptionally challenging in small biopsy/cytology specimens. Careful histologic evaluation of the tumor as well as the recognition of interstitial cells of Cajal will help the pathologist render the accurate diagnosis. • Male predominance is striking in upper GI leiomyomas. • Gastric leiomyomas occur in younger patients than esophageal leiomyomas. • Interstitial cells of Cajal exist in variable proportions in all upper GI leiomyomas. • Cells of Cajal can cause potential pitfall in the diagnosis of upper GI leiomyomas. • The recognition of Cajal cells will help pathologists render the accurate diagnosis. [ABSTRACT FROM AUTHOR]