INTRODUCTION
Merkel Cell Carcinoma (MCC) is a rare, life-threatening tumor with
neuroendocrine features. Due of its extremely low occurrence worldwide,
epidemiological data on the disease is limited.
(1). Commonly recognized risk factors
include fair skin, history of skin cancer, old age, chronic
immunosuppression, chronic ultraviolet (UV) light exposure, and Merkel
cell polyomavirus (MCPyV) infection (2).
Amongst these factors, MCPyV and UV exposure play a fundamental role
with synergistic effects in the pathophysiology of MCC
(3). Despite being a part of normal skin
flora in most individuals, MCPyV DNA can clonally combine with the
genome of neoplastic cell precursors at the initial phases of
carcinogenesis (4,
5). Concurrently, UV exposure elicits
antigen-presenting dendritic cells to produce inflammatory cytokines,
leading to local immunosuppression and creating an ideal environment for
tumoral growth (6). Moreover, immune
hypersensitivity from UV exposure facilitates the viral tumorigenic
process (2).
Merkel cells cannot be derived from the MCC because they lack the
ability to proliferate. Merkel cell precursors (perhaps generated from
epidermal stem cells or hair follicle stem cells) and pre- and pro-B
cells appear to have histopathology, genetics, and molecular
characteristics with malignant cells instead
(7).
MCC often presents as a single, asymptomatic erythematous or violaceous
nodule, often mistaken for cysts or abscesses. It usually originates
from the head or neck and generally spares the extremities
(8). Immunohistochemical (IHC) staining is
required to validate histopathological findings of small round cells
that infiltrate cutaneous or subcutaneous area.
(7). Although MCC responds to the
combination of excisional surgery, radiotherapy, and chemotherapy, it
requires continuous follow-ups within the first year of diagnosis due to
the high recurrence rate (9).
Here, we present a 32-year-old Iranian (non-Caucasian) immunocompetent
female with a small nodule on her left arm at the disease onset finally
diagnosed as MCC. In this report, we aim to emphasize the significance
of early diagnosis and management of this cancer and highlight the
complications that a late diagnosis would entail for these patients.