Testis and epididymis
Germ cell tumors
Carcinoid / Well differentiated neuroendocrine tumor

Author: Rafael Jimenez, M.D. (see Authors page)

Revised: 12 April 2017, last major update September 2012

Copyright: (c) 2002-2017, PathologyOutlines.com, Inc.

PubMed Search: carcinoid [title] well differentiated neuroendocrine tumor

Cite this page: Carcinoid / well differentiated neuroendocrine tumor. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/testiscarcinoid.html. Accessed September 25th, 2018.
Definition / general
  • Low grade neuroendocrine carcinoma, similar to counterpart at other sites
  • Usually monomorphic cells growing in solid nests, trabeculae or pseudoglands
  • Also called pure neuroendocrine carcinoma
  • Rare ( < 1% of testicular neoplasms), mean age 46 years
  • Carcinoid tumors are neuroendocrine tumors derived from enterochromaffin (Kulchitsky) cells that secrete serotonin and most commonly arise in GI and respiratory tracts
  • In testis, presumed to be a monodermal teratoma, although 20% have other teratomatous elements
Clinical features
  • Only 10% have clinical carcinoid syndrome
Prognostic factors
  • Metastatic disease is associated with carcinoid syndrome, tumor size 7 cm or more (Cancer 1993;72:1726)
Case reports
  • Excision; occasionally metastasizes
Gross description
  • Solid, yellowish tan, well circumscribed
  • Cysts reflect other teratomatous elements
Gross images

Images hosted on PathOut server:

Solid, tan cut surface

Microscopic (histologic) description
  • Islands of cells forming small acini; cords forming rosettes or sheets
  • Cells have granular eosinophilic cytoplasm, round nuclei with granular chromatin
  • Usually no intratubular germ cell neoplasia, no / minimal mitotic activity, usually minimal atypia or necrosis
Microscopic (histologic) images

Images hosted on PathOut server:

Well defined acini and
solid islands of cells
separated by fibrous stroma

Eosinophilic cytoplasm and
round nuclei with coarsely
granular chromatin

Images hosted on other servers:

Islands of tumor cells in lower right


Tumor cells have
eosinophilic cytoplasm
and salt and pepper chromatin

Insular pattern, chromogranin+

Intratubular germ cell neoplasia

Placental-like alkaline phosphatase

Various images

Cytology description
  • Isolated or sheets of tumor cells with granular cytoplasm, round nuclei, uniformly distributed fine chromatin
Negative stains
Electron microscopy description
  • Neurosecretory granules
Molecular / cytogenetics description
Differential diagnosis