Guidelines for Handling of Cytological Specimens in Cancer Genomic Medicine.

Rapid advances are being made in cancer drug therapy. Since molecularly targeted therapy has been introduced, personalized medicine is being practiced, pathological tissue from malignant tumors obtained during routine practice is frequently used for genomic testing. Whereas cytological specimens fixed mainly in alcohol are considered to be more advantageous in terms of preservation of the nucleic acid quality and quantity. This article is aimed to share the information for the proper handling of cytological specimens in practice for genomic medicine based on the findings established in "Guidelines for Handling of Cytological Specimens in Cancer Genomic Medicine (in Japanese)" published by the Japanese Society of Clinical Cytology in 2021. The three-part practical guidelines are based on empirical data analyses; Part 1 describes general remarks on the use of cytological specimens in cancer genomic medicine, then Part 2 describes proper handling of cytological specimens, and Part 3 describes the empirical data related to handling of cytological specimens. The guidelines indicated proper handling of specimens in each fixation, preparation, and evaluation.

HEG1, BAP1, and MTAP are useful in cytologic diagnosis of malignant mesothelioma with effusion.

BACKGROUND: The specificity and sensitivity of HEG1 for malignant mesothelioma (MM) is high. The use of BAP1/MTAP immunohistochemistry (IHC) is recommended to separate benign and malignant mesothelial proliferations. We determined how ancillary techniques can be used for the cytological diagnosis of MM with effusion. METHODS: Cell blocks from effusions from cases with MM, reactive mesothelial cells (RMCs), and carcinomas were analyzed by IHC with HEG1, BAP1, and MTAP and with homozygous deletion (HD) of CDKN2A by fluorescence in situ hybridization. Staining scores were calculated for IHC by adding the number of categories for the staining intensity and the staining extension. RESULTS: HEG1 was positive in all (41/41) MMs, but negative in carcinomas, except for ovarian carcinomas. Overall 76.9% (20/26) of RMCs and 28.6% (6/21) of ovarian carcinomas expressed HEG1. BAP1 loss was found in 71.1% of MMs, but none was found in RMCs. MTAP loss was found in 76.2% of MMs, but none was found in RMCs. 73.9% of MMs harbored HD of CDKN2A. There was concordance between loss of MTAP and HD of CDKN2A in 95% of MMs. CONCLUSION: HEG1 is a good marker for mesothelial differentiation in effusion cytology. HD of CDKN2A is frequently observed in cell blocks from effusions of MMs, and MTAP IHC may act as a surrogate for HD of CDKN2A. Cell block analysis is recommended for effusions of unknown origins with the following methods: IHC with HEG1 and claudin 4 to validate the mesothelial origin, followed by BAP1 and MTAP IHC to confirm malignancy.

Discriminant analysis of malignant mesothelioma and reactive mesothelium using three-dimensional nuclear estimation.

OBJECTIVE: The cytological diagnosis of coelomic fluid is essential for examining malignant mesothelioma (MM). However, reactive mesothelium (RM), caused by various factors, is morphologically similar to MM and thus often complicates the differential diagnosis. Here, nuclear luminance and steric alterations were assessed for the discriminant analysis of MM and RM. STUDY DESIGN: Thirteen epithelial MM and 11 RM cases were included. One hundred alterations in the numbers of nuclear pixels and focus layers and the coefficient of variation of nuclear luminance among layers were determined for each case to conduct discriminant analysis using the Mahalanobis distance. RESULTS: A cutoff value of 0.072 allowed highly accurate discrimination of MM (89.5%) and RM (89.6%). Fifteen cells appeared in 6 agglomerates of indiscriminable MM cases. The 6 agglomerates were individually examined. Malignant cells were dominant in 3 agglomerates (50%), allowing the discrimination of malignant cases. CONCLUSION: Discrimination using nuclear luminance and steric alterations is useful for morphologically indiscriminable MM cases. Three-dimensional analysis of agglomerates will be further investigated to improve the diagnostic accuracy.