Table 2.

Representative clinical and histopathological features of primary neuroendocrine carcinoma of the breast

Characteristic	Features
Epidemiologic
Age of diagnosis (years)	>50
Sex	Female>Male
Physical examination
Clinical presentation	Single palpable, well-circumscribed nodule (x̅: 2.5cm) or nipple discharge.
Nodal status	Non-palpable axillary lymph nodes
Carcinoid symptoms	Absent
Histopathology
Tumor components	Co-existing neuroendocrine and ductal cancer cell populations possibly from divergent differentiation of cancer stem cells (lobular or other types of breast cancer are rare).
Multifocality or multicentricity	Rare
Growth pattern	Solid carcinoid-like (most common), large cell-type, and small/oat cell-type
Cell type	Homogenous group of plasmacitoid, signet ring, clear cell, or small/oat cells
Histopathological features	Nuclear palisading; pseudorosette formation; loss of cell cohesion; intra- and/or extra-cellular mucin content; and abundant eosinophilic cytoplasm and nuclei with stippled (‘salt and pepper’) chromatin.
Diagnostic markers	Most sensitive and specific: chromogranin A or B and synaptophysin.
	Least specific: neurospecific enolase, CD56, neurofilament triplprotein, and bombin or leu.
Hormonal receptors	Estrogen/progesterone receptor positive
	HER2 negative
Molecular subgroup	Luminal A (basal-type has been documented)
Staging,	TisN0M0: 9 (10.9)
n (%) (N=82)a	T1NxM0: 35 (42.7)
	T2NxM0: 27 (32.9)
	T3NxM0: 8 (9.8)
	T4NxM0: 3 (3.7)

^a Based on case reports that specified size of the lesion; includes present case.