CDH1 Sequencing and Deletion/Duplication

Casandra

Casandra Test Code QD01419Version 1 (DRAFT)

Performing Lab

Lab Quest DiagnosticsLab Test ID 92568CPT Codes 81406, 81479

CDH1 Sequencing and Deletion/Duplication

Clinical Use

Use

This test is used to identify individuals with hereditary diffuse gastric cancer (HDGC) syndrome by detecting single‑nucleotide variants, deletions, and duplications in the CDH1 gene. It is indicated for individuals with a personal or family history of diffuse gastric cancer or lobular breast cancer, with genetic counseling and informed consent strongly recommended before testing. The person in the family with the earliest or youngest age–related diagnosis should ideally be tested first. Positive (pathogenic or likely pathogenic) results confer a significantly increased lifetime risk of diffuse gastric cancer (up to ~83% for women, ~67% for men) and elevated risk of lobular breast cancer in women (~39–52%), and NCCN guidelines recommend enhanced surveillance, prophylactic surgery, and genetic counseling for family members. Negative and VUS results must be interpreted in the context of personal and family history, and variant interpretation may change over time.

Special Instructions

Informed consent following genetic counseling is strongly recommended. Testing should prioritize the family member with the earliest or youngest age at diagnosis. If a familial CDH1 mutation is known, consider ordering the Hereditary Cancer Single Site(s) test (test code 93945) instead. Genetic counseling is available through Quest Genomics Client Services. Insurance coverage will be verified upon receipt of a completed order; if estimated patient responsibility exceeds $100, you and/or the patient will be notified prior to test initiation. A fully completed family history form and order, and any required preauthorization, are important for timely processing.

Limitations

Negative results do not rule out hereditary cancer predisposition; implications depend on personal and family history. VUS findings have uncertain significance and require careful interpretation. Variant classification may evolve over time, and checking for updates (e.g., via VariantIQ) is advised. The test is limited to CDH1; other hereditary cancer risks may require additional testing. Additional testing may be necessary based on incomplete assessment or evolving classification.

Test Details