Cellular Classification
of SCLC
Before initiating treatment of a
patient with small cell lung cancer (SCLC), an experienced lung cancer
pathologist should review the pathologic material.
Pathologic Classification
The current classification of
subtypes of SCLC includes the following:[1]
·
Small cell carcinoma.
·
Combined small cell carcinoma (i.e.,
SCLC combined with neoplastic squamous and/or glandular components).
SCLC arising from neuroendocrine
cells forms one extreme of the spectrum of neuroendocrine carcinomas of the
lung.
Neuroendocrine tumors include the
following:
·
Low-grade typical carcinoid.
·
Intermediate-grade atypical
carcinoid.
·
High-grade neuroendocrine tumors including
large-cell neuroendocrine carcinoma (LCNEC) and SCLC.
Because of differences in clinical
behavior, therapy, and epidemiology, these tumors are classified separately in
the World Health Organization (WHO) revised classification. The variant form of
SCLC called mixed small cell/large cell carcinoma was not retained in the
revised WHO classification. Instead, SCLC is now described with only one
variant, SCLC combined, when at least 10% of the tumor bulk is made of an
associated non-small cell component.
SCLC presents as a proliferation of
small cells with the following morphological features:[2]
·
Scant cytoplasm.
·
Ill-defined borders.
·
Finely granular "salt and
pepper" chromatin.
·
Absent or inconspicuous nucleoli.
·
Frequent nuclear molding.
·
A high mitotic count.
Combined small cell carcinoma
includes a mixture of small cell and large cell or any other non-small cell
component. Any cases showing at least 10% of SCLC are diagnosed as combined
SCLC, and SCLC is limited to tumors with pure SCLC histology. SCLC associated
with LCNEC is diagnosed as SCLC combined with LCNEC.
Nearly all SCLC are immunoreactive
for keratin, thyroid transcription factor 1, and epithelial membrane antigen.
Neuroendocrine and neural differentiation result in the expression of dopa
decarboxylase, calcitonin, neuron-specific enolase, chromogranin A, CD56 (also
known as nucleosomal histone kinase 1 or neural-cell adhesion molecule),
gastrin-releasing peptide, and insulin-like growth factor 1. One or more
markers of neuroendocrine differentiation can be found in approximately 75% of
SCLC.[3]
Although preinvasive and in
situ malignant changes are frequently found in patients with non-small
cell lung cancer, these findings are rare in patients with SCLC.[4]
References
1.
Travis WD, Colby TV, Corrin B, et
al.: Histological typing of lung and pleural tumours. 3rd ed. Berlin:
Springer-Verlag, 1999.
2.
Brambilla E, Travis WD, Colby TV, et
al.: The new World Health Organization classification of lung tumours. Eur
Respir J 18 (6): 1059-68, 2001. [PUBMED Abstract]
3.
Guinee DG Jr, Fishback NF, Koss MN,
et al.: The spectrum of immunohistochemical staining of small-cell lung
carcinoma in specimens from transbronchial and open-lung biopsies. Am J Clin
Pathol 102 (4): 406-14, 1994. [PUBMED Abstract]
4.
Kumar V, Abbas A, Fausto N, eds.:
Robins and Cotran Pathologic Basis of Disease. 7th ed. Philadelphia, Pa:
Elsevier Inc, 2005.
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