Context: The diagnosis of sarcomatoid neoplasms of the lung and pleura can be challenging. Homozygous deletion of 9p21, the locus harboring the p16 gene, has been reported as the most common genetic alteration in malignant mesotheliomas that is of potential diagnostic and prognostic significance.
Objectives: To evaluate the frequency of 9p21 deletion by fluorescence in situ hybridization in the primary sarcomatoid neoplasms of the lung and pleura and to determine its potential diagnostic utility.
Design: Ninety-two sarcomatoid neoplasms of the lung and pleura (32 sarcomatoid mesotheliomas, 15 sarcomatoid carcinomas, 32 solitary fibrous tumors, and 13 high-grade sarcomas) were examined for 9p21 deletion by fluorescence in situ hybridization.
Results: Deletion of 9p21 was most frequently seen in malignant mesotheliomas (81%), followed by sarcomatoid carcinomas (53%), sarcomas (25%), and solitary fibrous tumors (12.5%). Malignant mesotheliomas showed mostly homozygous deletion, whereas sarcomatoid carcinomas showed either homozygous or hemizygous deletion. None of the sarcomas showed homozygous deletion. There was a trend toward more frequent occurrence of 9p21 deletion in recurrent solitary fibrous tumors, but this did not reach statistical difference.
Conclusions: Deletion of 9p21 is common in sarcomatoid tumors of the lung and pleura. Despite statistically significant differences in the frequency of 9p21 deletion, and because of the large overlap among the study groups, this genetic abnormality cannot be used as a reliable diagnostic tool in the assessment of sarcomatoid lesions of the lung and pleura. A potential use of p16 deletion in predicting the biology of solitary fibrous tumors should be further explored.