Primary mucinous carcinoma of the skin (PMCS) is a rare malignant neoplasm of the sweat gland origin. It was first described by Lenox et al. in 1952 and was later named by Mendoza and Helwig in 1971 by summarizing the clinical and histological characteristics based on observations of 14 cases. The tumor is extremely rare with approximately one case in every 150, 000 specimens of cutaneous lesions. Histogenesis is still debated, and apocrine, eccrine, and more recently, neuroendocrine origins have been proposed, as the understanding of the entity continues to evolve. It commonly involves the head and neck especially periorbital region and presents as an asymptomatic, slow-growing, well-circumscribed mass that is often diagnosed clinically as a benign lesion. Pathologically, these tumors may be mistaken for more common metastatic mucinous carcinomas; hence, immunohistochemical markers are essential to aid in establishing a definite diagnosis. Recently, some investigators have described an in-situ component of PMCS, which is considered a precursor of PMCS. The presence of an in-situ component is useful in distinguishing PMCS from metastatic mucinous lesions. The pathological and immunohistologic features of this rare cutaneous neoplasm will be discussed along with a review of the literature. Differential diagnoses, possible histogenesis, electron microscopic findings, clinical behavior, management, and prognostic factors will also be discussed.

Dr. Mukund Tinguria is working as Pathologist in the Department of Pathology and laboratory Medicine at the Brantford General Hospital, Brantford, Ontario, Canada. He is primarily involved in surgical pathology and cytology diagnostic work. His areas of interest include head and neck, gastrointestinal, breast, genitourinary pathology, and cytology. He also works as a Part Time Teaching Faculty for the McMaster University, Hamilton, Canada and is involved in undergraduate and postgraduate training. He has been awarded the excellence in teaching award by the McMaster University in 2022. He has many publications to his credit and works on the editorial board of some reputed medical journals.