title: Primary retroperitoneal Merkel cell carcinoma: Case report and literature review.
abstract: BACKGROUND
  Merkel cell carcinoma (MCC) is an aggressive cutaneous neuroendocrine carcinoma that affects elderly patients and typically arises in sun-exposed skin. The disease is very rare and only few cases present with no apparent skin lesion. In the retroperitoneum there are only two cases reported in the literature.
  
  
  METHODS
  We report a case of a 54-year-old Mexican male with MCC, which presented as a large retroperitoneal mass. Pathological and immunohistochemical analysis of the transabdominal CT-guided biopsy specimen revealed a MCC. The patient underwent preoperative chemotherapy followed by a laparotomy and the mass was successfully excised.
  
  
  CONCLUSIONS
  There are two possible explanations for what occurred in our patient. The most plausible theory is the retroperitoneal mass could be a massively enlarged lymph node where precursor cells became neoplastic. This would be consistent with a presumptive diagnosis of primary nodal disease. Moreover, metastasis to the retroperitoneal lymph nodes has been reported as relatively common when compared to other sites such as liver, bone, brain and skin. The less probable theory is the non-described "regression" phenomena of a cutaneous MCC, but we are not found a primary skin lesion.
  
  
  CONCLUSIONS
  Preoperative chemotherapy and excision of the primary tumor is the surgical treatment of choice for retroperitoneal MCC. We propose that further studies are needed to elucidate the true efficacy of chemotherapy in conventional and unconventional patients with MCC.
authors.affiliation: Surgical Department of Gastrointestinal Tumors, National Cancer Institute, Mexico City, Mexico.
authors.forename: Osvaldo A
authors.initials: OA
authors.lastname: Quiroz-Sandoval
authors.affiliation: Surgical Department of Bone and Soft Tissue Sarcomas, National Cancer Institute, Mexico City, Mexico.
authors.forename: Mario
authors.initials: M
authors.lastname: Cuellar-Hubbe
authors.affiliation: Anatomic Pathology Department of Gastrointestinal Tumors, National Cancer Institute, Mexico City, Mexico. Electronic address: Saul.lino.sil@gmail.com.
authors.forename: Leonardo S
authors.initials: LS
authors.lastname: Lino-Silva
authors.affiliation: Surgical Department of Gastrointestinal Tumors, National Cancer Institute, Mexico City, Mexico.
authors.forename: Rosa A
authors.initials: RA
authors.lastname: Salcedo-Hernández
authors.affiliation: Surgical Department of Gastrointestinal Tumors, National Cancer Institute, Mexico City, Mexico.
authors.forename: Horacio N
authors.initials: HN
authors.lastname: López-Basave
authors.affiliation: Surgical Department of Gastrointestinal Tumors, National Cancer Institute, Mexico City, Mexico.
authors.forename: Alejandro E
authors.initials: AE
authors.lastname: Padilla-Rosciano
authors.affiliation: Surgical Department of Gastrointestinal Tumors, National Cancer Institute, Mexico City, Mexico.
authors.forename: Alberto M
authors.initials: AM
authors.lastname: León-Takahashi
authors.affiliation: Surgical Department of Gastrointestinal Tumors, National Cancer Institute, Mexico City, Mexico.
authors.forename: Ángel
authors.initials: Á
authors.lastname: Herrera-Gómez
keywords: CK20; Cancer; Immunohistochemistry; Merkel cell; Retroperitoneal