Clinicopathologic and immunohistochemical characteristics of upper gastrointestinal leiomyomas harboring interstitial cells of Cajal: A potential mimicker of gastrointestinal stromal tumor

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.