Multiplatform assessment of anaplastic lymphoma kinase (ALK) gene rearrangement in signet ring cell carcinoma of the gastrointestinal tract.

Abstract

e14612 Background: ALK-EML4 translocation is an established driver aberration in NSCLC, with reported predilection for cases with signet ring histology. We assessed the presence of ALK gene rearrangements in signet ring cancers arising in the stomach and colon. Methods: Histologically confirmed cases of signet ring adenocarcinoma of the stomach or the colon were identified from the pathology archive of Emory University Hospital. Presence of the classic ALK and EML4 fusion gene was initially determined by fluorescence in-situ hybridization (FISH) method. Cases showing break-apart signal in more than 15% of enumerated cells were considered positive; at least 10% of enumerated cells was considered “possibly positive”. Immunohistochemistry of the fused gene product was assessed using previously validated antibodies ALK1 clone (1:100; DAKO) and 5A4 (Novocastra, Leica Biosystems) and positive controls of ALK-translocated lung cancer. Positive or possibly positive cases by FISH were further analyzed by RT-PCR using specific primers for the most common translocation pairs (EML4 Ex13/ALK Ex20 and EML4 Ex6/ALK Ex20) along with positive (H228, HEK293) and negative (H460, H1975) control cell lines. Results: We retrieved 44 cases of signet ring carcinoma diagnosed between 2001 and 2011; 26 gastric and 18 colon cancer. Median age - 63 yrs; M/F 17/27; Black - 47.5%; White - 47.5%; Others - 5%; Stage I - 21.4%; II - 31%; III - 26.2; IV - 21.4%. One of 44 cases (2.3%) was positive for ALK translocation by FISH using the standard criteria of at least 15% positive cells for the break-apart signal (50-70 cells counted per case). 7 cases (16%) were considered possibly positive [1 of 18 (6%) colon cancer and 6 of 26 (26%) gastric cancer cases]. IHC showed 0 of 44 (0%) cases positive. Molecular analysis using RT-PCR did not confirm the suspected ALK gene rearrangements in any of the 7 cases considered possibly positive by FISH. Conclusions: The overall frequency of ALK gene rearrangement detected by FISH in signet ring cancer of the GI tract was low, but appears comparable to the reported frequency in lung cancer. Signet ring histology failed to enrich for cases with ALK gene translocation in this histologic subtype.