Molecular Diagnostic Tests Frequently Requested

Malignant Lymphoma - Clonal Rearrangement Analysis:

Diagnosis of lymphoma can be very difficult in some cases. Molecular evaluation for evidence of immunoglobulin (Ig) or T-cell receptor gene rearrangements is important in establishing so-called clonality. Monoclonality generally correlates with lymphoma and polyclonality is consistent with benign reactive conditions. As such, this molecular information can be used in the following ways: confirming lymphoma diagnosis; lineage assignment of lymphoma (B or T cell); and identification of lymphoma-specific markers (e.g., specific rearrangement) for potential post-treatment follow-up.

Colon Cancer And HNPCC - Microsatellite Instability Testing:

Hereditary non-polyposis colon cancer (HNPCC) is caused by germline mutations in mismatch repair (MMR) genes, resulting in genomic microsatellite instability (MSI). The presence of MSI in a tumor suggests the possibility of a germline mutation in one of the MMR genes and further mutational analysis is then recommended. MSI may also be seen in sporadic colorectal cancers due to acquired hypermethylation of DNA mismatch repair gene. Colorectal cancers with MSI, either HNPCC- associated or sporadic, have been reported to be associated with a better prognosis. Furthermore, recent studies reported that fluorouracil-based adjuvant chemotherapy was only effective in individuals with microsatellite stable colon cancers. In conjunction with complementary immunohistochemistry, MSI molecular testing helps not only to identify HNPCC patient, but also to provide guidance for adjuvant chemotherapy to colorectal cancer patients.

Breast Cancer And Herceptin Treatment - Her-2/Neu Testing By FISH:

Amplification of HER-2/neu oncogene or overexpression of HER-2/neu protein is a significant adverse prognostic indicator in patients with lymph node-positive breast cancer.  More importantly, the amplification predicts the therapeutic response to the drug Herceptin. More recently, patients with early stage, HER-2/neu amplified breast cancers have been found to have a significant reduction rate of recurrence upon Herceptin treatment. Current clinical practice utilizing Herceptin requires the demonstration of HER-2/neu amplification or HER-2/neu protein overexpression in invasive cancer cells.

Glioma Diagnosis And Prognostication - Chromosome 1p19q Deletion By FISH:

The relative incidence of the diagnosis of gliomas as oligodendroglioma and astrocytoma varies widely between institutions indicating that diagnostic criteria differ and/or are difficult to apply. Because separation of astrocytomas from oligodendrogliomas has prognostic and therapeutic importance, reproducible and definitive criteria are needed for their separation. Loss of chromosomal arms 1p or 19q is characteristic of oligodendrogliomas and combined loss of both 1p and 19q is considered diagnostic of oligodendrogliomas. Moreover, loss of 1p may identify treatment-sensitive gliomas including anaplastic oligodendroglioma, and patients with tumor having combined chromosome 1p and 19q loss appear to have a particularly favorable prognosis.

Fluorescence In-Situ Hybridization In Detection Of Chromosomal Translocation In Various Solid Tumors And Lymphomas:

A significant number of sarcomas, lymphomas and leukemias have consistent chromosomal abnormalities that are detectable by standard cytogenetics or molecular genetic approaches.   It is also clear that these sarcomas and lymphomas should be defined by their specific molecular and cytogenetic alterations, although it is important to determine the sensitivity and specificity of these translocations for specific tumor subtypes and the relative roles of molecular and histological classification of each sarcoma. FISH provides a powerful diagnostic modality to demonstrate a specific gene fusion or chromosomal alteration. Metaphase chromosomal preparation from the tumor can be used to demonstrate translocations by chromosomal painting using chromosome specific probes or gene specific probes. However, this is not always possible since cell culture of tumor tissue to obtain metaphase chromosomes may be unsuccessful. In these cases, interphase FISH provides an excellent alternative using touch preparations from fresh or frozen tumor specimens without the requirement for tissue culture. One major advantage of interphase FISH over traditional karyotyping is the ability to detect cryptic gene rearrangements.

Tissue DNA Genotyping In Diagnosis And Subtyping Of Hydatidiform Moles:

Molar gestations are defined at the genetic level by their unique parental chromosomal compositions. Their diagnosis, however, currently relies largely on histological features and on the occasional support of ancillary immunohistochemical and DNA ploidy analyses. Recently we have validated STR-DNA genotyping for the routine diagnosis and subtyping of hydatidiform moles. This genetic diagnostic evaluation is a practical and cost-effective method which uses a minimal amount of template DNA extracted from paraffin embedded, formalin fixed tissue, followed by a single multiplex PCR amplification and high resolution product analysis through capillary electrophoresis. This “one-stop shopping” approach is highly sensitive and specific and has become part of the routine work-up of hydatidiform moles at Yale Pathology.