Incidental Renal Langerhans Cell Histiocytosis Within Clear Cell Renal Carcinoma: A Case Report and Literature Review

Langerhans cell histiocytosis (LCH) is a disease characterized by the excessive proliferation and abnormal differentiation of immune cells, including monocytes, T cells, and dendritic cells. The most affected organs are the bones, skin, lungs, liver, and spleen, while renal involvement is rare. LCH primarily affects children and is seldom diagnosed in adults. In this case report, we describe a 64‐year‐old man patient with no prior urological history nor history of LCH and presenting with both localized renal LCH and clear cell renal carcinoma (ccRCC). Renal cancer was first discovered fortuitously on an abdominal computed tomography (CT) scan while the patient presented symptoms of a complicated urinary tract infection. Following radical nephrectomy, LCH foci was detected as incidental histological finding within the ccRCC pathological analysis. Immunohistochemical staining confirmed the positivity of S‐100 and CD1a markers and PCR analysis identified the BRAF V600E mutation. Based on these findings, a diagnosis of ccRCC associated with LCH was established.