Small cell carcinoma of salivary gland

Epidemiology

Small cell carcinoma of the salivary gland accounts for less than 1% of salivary gland tumours2, less than 2% of salivary gland malignancies. They are found predominantly in major salivary glands, particularly the parotid gland. There is a male predominance, with a peak incidence in the fifth to seventh decades. The lack of positivity for the Merkel cell polyomavirus in primary parotid high-grade neuroendocrine carcinoma, whether or not positive for CK20, argues that these tumours are distinct from Merkel cell carcinoma4.

Histopathology

The tumour is composed of small cell with scant cytoplasm; nuclei have fine chromatin and lack nucleoli.

This is probably a heterogeneous group of tumours with variable immunophenotypes:

	Merkel cell type	Pulmonary type	Ductal type
nuclear morphology	plump, delicate chromatin, pale, "washed out", nuclear moulding not prominent	elongated with dense chromatin and nuclear moulding. crush artefact is common.
architecture		pseudorosettes and fibrillary cytoplasm	focal glandular and/or squamous differentiation

Immunohistochemistry

	Overall	Merkel cell type	Pulmonary type	Ductal type
pan-cytokeratin	14/15(dot-like in 10 cases)2	positive	positive	positive
AE1/3	14/15(dot-like in 9 cases)2
Cam5.2	13/15(dot-like in 10 cases)2
EMA	14/152
CK7	5/15(dot-like in 3 cases)2
CK20	3/51, 11/152	positive	negative	negative
synaptophysin	10/152	positive	positive	negative
chromogranin	13/152	positive	positive	negative
neurofilament	6/152
CD56	5/152
CD57	4/152
NSE	15/152
p53	8/15(diffusely positive)2
CEA	4/152
TTF-1	3/152	negative in most of the few cases studied
S-100	0/152
HHF-35	0/152
SMA	0/152
vimentin	0/152
LCA	0/152
HMB-45	0/152

Differential diagnosis

solid variant of adenoid cystic carcinoma: has a focal cribriform pattern and has myoepithelial but lacks neuroendocrine differentiation.
lymphoma: positive for LCA, negative for cytokeratins.
melanoma: positive for S-100.
large cell undifferentiated carcinoma: may show neuroendocrine differentiation; nucleoli are conspicuous.
metastatic pulmonary small cell carcinoma: negative for CK20.
metastatic Merkel cell carcinoma: shows positivity for the Merkel cell polyomavirus.

Prognosis

More than half of patients develop lymph node and/or distant metastases2. Two and five year survivals are 38 to 70% and 13 to 46% respectively, which is superior to small cell carcinoma of the lung and larynx. CK20-positive (Merkel cell type) small cell carcinoma of salivary glands may have a better prognosis2.

References

Diagnostic histopathology of tumors. Edited by CDM Fletcher. 2nd edition. Churchill Livingstone. Page 283.

1 Chan, J. K., S. Suster, et al. (1997). "Cytokeratin 20 immunoreactivity distinguishes Merkel cell (primary cutaneous neuroendocrine) carcinomas and salivary gland small cell carcinomas from small cell carcinomas of various sites." Am J Surg Pathol 21(2): 226-34.

2 Nagao, T., T. A. Gaffey, et al. (2004). "Small cell carcinoma of the major salivary glands: clinicopathologic study with emphasis on cytokeratin 20 immunoreactivity and clinical outcome." Am J Surg Pathol 28(6): 762-70.

3 Cheuk W,Chan JK. Advances in salivary gland pathology. Histopathology 2007; 51:1-20

4 Chernock RD, Duncavage EJ, Gnepp DR, El-Mofty SK, Lewis JS, Jr. Absence of Merkel cell polyomavirus in primary parotid high-grade neuroendocrine carcinomas regardless of cytokeratin 20 immunophenotype. Am J Surg Pathol. 2011 Dec;35(12):1806-11.

This page last revised 15.7.2007.