Thymic Carcinoma Arising in Thymoma

Malignant transformation is often associated with areas of necrosis and necrosis should induce a search of transformation. The combinations are very variable, but various papers describe:

conventional types of thymoma (i.e., lymphocyte-rich, epithelial-rich, or mixed) with well-differentiated squamous cell carcinoma2,3,4
conventional types of thymoma with poorly differentiated squamous cell carcinoma2
spindle-cell thymoma with poorly differentiated squamous cell carcinoma2,5

There is very little information on the immunophenotypes of the components of a thymoma that has transformed to thymic carcinoma:

Case		CK7	CK8	CK18	CK19	EMA	CD5	Vimentin	CD99+ lymphocytes	p53, % of tumour nuclei positive

11	large polygonal cell thymoma (type B2?)	(+)	-	-	+	(+)	-	-	yes	15%, weak
11	undifferentiated carcinoma	+	++	(+)	++	++	-	-	few	>90%, strong

21	large polygonal cell thymoma (type B2?)	-	-	-	(+)	-	-	-	yes	80%, weak
21	undifferentiated carcinoma	++	(+)	(+)	+	+++	-	+++	no	90%, strong

31	spindle cell thymoma (type A?)	(-)	(+)	(+)	+++	(+)	-	-	yes	0%
	squamous carcinoma	++	+++	+++	+++	++	+	-	no	20%, strong
	clear cell carcinoma	-	+	+	+	+	-	-	no
	poorly differentiated carcinoma	-	-	-	-	-	-	-	no

41	squamoid thymoma (type B3?)	(+)	+	(+)	+++	++	+	-	yes	5%, weak
41	spindle cell carcinoma	(+)	+	+	+++	(+)	-	-	no	10%, weak

51	squamoid thymoma (type B3?)	-	-	-	+++	-	-	-	yes	10%, weak
51	moderately differentiated squamous cell carcinoma	-	-	-	+++	(+)	-	-	no	20%, strong

(+) = focally positive, + = weakly positive, ++ = moderately positive, +++ = strongly positive

References

1 Kuo TT,Chan JK. Thymic carcinoma arising in thymoma is associated with alterations in immunohistochemical profile. Am J Surg Pathol 1998; 22:1474-81

2 Suster S,Moran CA. Primary thymic epithelial neoplasms showing combined features of thymoma and thymic carcinoma. A clinicopathologic study of 22 cases. Am J Surg Pathol 1996; 20:1469-80

3 Salyer WR,Eggleston JC. Thymoma: a clinical and pathological study of 65 cases. Cancer 1976; 37:229-49

4 Morinaga S, Sato Y, Shimosato Y, et al. Multiple thymic squamous cell carcinomas associated with mixed type thymoma. Am J Surg Pathol 1987; 11:982-8

5 Kuo TT, Chang JP, Lin FJ, et al. Thymic carcinomas: histopathological varieties and immunohistochemical study. Am J Surg Pathol 1990; 14:24-34

This page last revised 20.6.2005.