Appendiceal Carcinoid / Well Differentiated Neuroendocrine Neoplasm / Tumor

Differential Diagnosis

Appendiceal Carcinoid / Well Differentiated Neuroendocrine Cell Neoplasm	Appendiceal or Other GI Adenocarcinoma
Bland cytologic features	Atypical cytology
Chromogranin or synaptophysin positive	Chromogranin and synaptophysin negative
No desmoplastic response	Desmoplastic response frequent
Rare mitotic figures	Mitotic figures frequently numerous
Cohesive nests and cords	Frequent single cell infiltration
No surface adenoma or in situ lesion	May have surface adenoma or in situ component
No intracytoplasmic mucin	May have intracytoplasmic mucin and/or signet ring cells

Appendiceal Carcinoid / Well Differentiated Neuroendocrine Cell Neoplasm	Goblet Cell Carcinoid and/or Carcinoma ex-GCC
Chromogranin or synaptophysin positive	Chromogranin and synaptophysin stain rare to scattered cells only
No intracytoplasmic mucin (lumenal mucin may be present in tubular carcinoid)	Intracytoplasmic mucin in goblets
CK7 negative, CK20 variable	CK7 variable, CK20 100%
Rare mitotic figures at most	Mitotic figures may be numerous in carcinoma ex-GCC
Cohesive nests and cords	Single cell infiltration or sheet like growth in carcinoma ex-GCC
No desmoplasia	Desmoplasia may be present in carcinoma ex-GCC

Determination of common sites of origin for metastatic well differentiated endocrine neoplasms

Detection of specific islet hormones may be useful; PAX8 data has been questioned (see Pancreas).

Determination of common sites of origin for metastatic well differentiated endocrine neoplasms-keratins

CK7/20 staining is only helpful in instances of positivity where a negative result is expected