Isolated Langerhans cell histiocytosis of the stomach in adults: An analysis of clinicopathologic characteristics and molecular genetics.

Isolated gastric Langerhans cell histiocytosis (LCH) occurs extremely rarely in adults. We characterized the clinicopathological and molecular genetics of this rare entity. We retrospectively analyzed the clinicopathologic and prognostic features of 3 patients with isolated gastric LCH during the past 10 years, with a review of an additional 20 patients from the literature. A total of 23 patients with isolated gastric LCH were included in this study. There were 15 males and 8 females, with a mean age of 44.5 (median, 48; range, 21-68) years. Stomach discomfort and abdominal pain were the most common presenting symptoms. The lesions were mainly concentrated in the gastric body and antrum (21/23). Gastroscopy often revealed an elevated lesion/polyp. Molecular tests showed that BRAF-V600E gene mutations were found in 10/11 (42%) patients, while none of the patients (0/5) harbored KRAS gene mutations. None of the 23 patients received further treatment. Twenty patients had follow-up results (from 4 to 66 months). One patient with atypical morphological features died of unknown cause 2 months after removal of the tumor. One patient was found to have secondary lesions in the skull and axillary region. The other 18 patients survived without any evidence of disease progression during the follow-up period. In the daily diagnosis of gastroscopic biopsy, it is necessary to be aware of the possibility of LCH in patients with lesions in the gastric body or antrum if endoscopy reveals bulge/polypoid changes and heavy microscopic inflammation. In addition, we should be alert to the possibility of LCH with malignant transformation if the histological morphology exhibits tumor cell nucleoli and mitotic figures or necrosis. The immunohistochemical marker CD56 may help differentiate between LCH and Langerhans cell sarcoma when the morphology is difficult to determine. Molecular detection has shown that the mutation rate of BRAF in gastric LCH is up to 90.9%; more work is needed as the number of cases is small. Current data show a good prognosis for isolated gastric LCH in adults, but long-term follow-up for early detection of disease progression or systemic involvement is necessary.