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HER2/neu gastric cancer by FISH

Test Code

FP HER2 GA

Associations

Gastric and gastroesophageal junction (GEJC) cancer;

Herceptin

Methodology

Fluorescence in situ Hybridization (FISH)

Turnaround Time

3-5 days

Specimen Requirements

10% neutral buffered formalin fixed paraffin embedded tissue
5 mm^3 fresh tissue or 3.0 mL (min. 2.0 mL) FNA in MPLN RPMI media

Specimen Stability
Paraffin blocks stable at 18-25°C indefinitely
Fresh tissue or FNA stable at 2-8°C for 72 hours
Storage & Handling

Fresh tissue, FNA or paraffin embedded tissue, ship in a Styrofoam container with a cool/refrigerated pack (Do not allow cool pack to directly contact sample)

Causes for Rejection

Improper specimen labeling; Insufficient sample; Inadequate fixation and/or processing

Reference Range

A positive FISH result (HER2/CEP17 ratio greater or equal to 2.0) or an IHC score of 3+ provides eligibility for Herceptin. Patients with IHC scores of 0/1 should not be treated with Herceptin. IHC score of 2+ should be retested using FISH. Any equivocal cases should be retested by an alternate method.

Description

The FDA recently approved trastuzumab (Herceptin, Genentech) for use in combination with cisplatin and capecitabine or 5-fluorouracil to treat patients with human epidermal growth factor receptor 2 (HER2)-over expressing (also called HER2-positive) metastatic gastric or GEJC who have not received prior treatment for metastatic disease.
The new indication was largely based upon the results of the “Trastuzumab for Gastric Cancer” or ToGA trial (Lancet. August 28, 2010). The trial revealed that patients on trastuzumab plus chemotherapy had a median overall survival of 13.8 months compared to 11.1 months with chemotherapy alone. However, stratifying the HER2+ group into two subgroups (a) FISH+ and IHC-negative (IHC0 or IHC1+) vs. (b) IHC3+ or ICH2+FISH+ revealed more distinct 11.8 month and 16.0 month median overall survivals,  respectively. FISH-positivity alone did not indicate Herceptin benefit; Herceptin benefit was essentially limited to immunohistochemically 3+ gastric cancers or IHC2+ and FISH+ cancers.

IHC or FISH can be used as the first-line testing method, but based on ToGA data and pending future investigations, oncologists should consider immunohistochemistry for optimal frontline testing.

References
  1. Albarello L, Pecciarini L, Doglioni C. (2011) Adv Anat Pathol. 18(1):53-9. HER2 Testing in Gastric Cancer.
  2. Ruschoff J et al. (2010) HER2 diagnostics in gastric cancer – guideline validation and development of standardized immunohistochemical testing. Virchows Arch. 457(3):299-307.
  3. Gravalos C, Jimeno A. (2008) HER2 in gastric cancer: a new prognostic factor and a novel therapeutic target. Ann Oncol. 9:1523-9.