The MTAP gene is located on the telomeric side of CDKN2A on chromosome 9p21. Its protein product, MTAP, is critical for polyamine metabolism and the salvage of adenine and methionine.

• Loss of MTAP protein expression is a reliable marker for mesothelioma
• Malignant melanomas have decreased MTAP staining compared to melanocytic nevi
• Loss of MTAP immunoreactivity has been suggested as a possible predictive surrogate for CDKN2A HD in IDH-mutant astrocytoma

Prepare a formalin-fixed, paraffin embedded (FFPE) tissue block

FFPE tissue block

Tissue section mounted on a charged, unstained slide

Ambient (preferred)

• Unlabeled/mislabeled
• Insufficient tissue
• Slides broken beyond repair

Immunohistochemical staining and microscopic examination

If requested, an interpretive report will be provided.

Specifications

The MTAP gene is located on the telomeric side of CDKN2A on chromosome 9p21. Its protein product, MTAP, is critical for polyamine metabolism and the salvage of adenine and methionine.

Staining patterns

Tumor cells are negative for cytoplasmic staining. Endothelial cells serve as an internal positive control.

MTAP retention:

Characterized by cytoplasmic staining in tumor cells. Cytoplasmic staining for MTAP is present in all normal human tissues. Nuclear staining is considered nonspecific.

MTAP loss:

Defined by absence of cytoplasmic staining in tumor cells in the presence of a positive internal control. Nuclear staining is considered nonspecific.

References

1. Chapel, DB Schulte JJ, Berg K et al. MTAP immunohistochemistry is an accurate and reproducible surrogate for CDKN2A fluorescence in situ hybridization in diagnosis of malignant pleural mesothelioma. Modern Pathology 2020;33:245-254. PMID: 31231127 DOI: 10.1038/s41379-019-0310-0
2. Berg KB, Churg AM, Cheung S et al. Usefulness of methylthioadenosine phosphorylase and BRCA-Associated protein 1 immunohistochemistry in the diagnosis of malignant mesothelioma in effusion cytology specimens. Cancer Cytopathology 2020;128(2)126-132. PMID: 31821740 DOI: 10.1002/cncy.22221
3. Satomi K, Ohno M, Matsushita Y et al. Utility of methylthioadenosine phosphorylase immunohistochemical deficiency as a surrogate for CDKN2A homozygous deletion in the assessment of adult-type infiltrating astrocytoma. Modern Pathology 2021;34(4):688-700. PMID: 33077924 DOI: 10.1038/s41379-020-00701-w