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In summary we identified a novel
In summary, we identified a novel MLPH-ALK fusion in AST with discordant results of ALK IHC. In order not to overlook ALK-rearranged AST with rare fusion partners on IHC screening, a sensitive IHC method is preferable.
Introduction
Lung cancer remains the leading cause of cancer related deaths worldwide [1]. In the last decade there have been important advances in oncogene-driven non-small cell lung cancer (NSCLC).
For the first time, Soda reported in 2007 the presence of fusion between the ALK gene and the Echinoderm microtubule-associated protein-like 4 (EML4) gene in NSCLC [2]. This fusion arises from an herpes simplex virus 2 in the short arm of chromosome 2 [inv (2) (p21p23)] by linking the exons 1–13 of the EML4 gene to the exons 20–29 of the ALK gene. As a consequence of this rearrangement, a chimeric fusion protein is encoded with its constitutively activated tyrosine kinase domain, which generates the activation of intracellular signaling pathways and consequently increased cell growth, proliferation and survival. Since then, several variants of that translocation have been identified [3,4]. ALK rearrangements are found in approximately 3% to 7% of NSCLCs [[5], [6], [7]] and studies have shown they are more frequent in younger, non or light smokers with adenocarcinomas subtype [8]. Lung cancers harboring EML4–ALK translocation are highly sensitive to ALK tyrosine kinase inhibitors with successful clinical results [9,10].
There are several available methods to test the ALK rearrangement, including fluorescence in situ hybridization (FISH), immunohistochemistry (IHC) and reverse transcriptase polymerase chain reaction (RT-PCR), being break-apart ALK FISH assay the gold standard for screening, despite limitations regarding their use in clinical practice [7].
Materials and methods
Results
From a total of 183 non-squamous NSCLC samples that were analyzed, 131 could perform FISH test, finding 123 (93.9%) negative and 8 (6.1%) positive patients (Fig. 1). These eight FISH-positive cases were also positive for ALK by immunohistochemistry. Fifty-one samples were not evaluable by FISH, 35 because of technical problems such as insufficient number of cells and 16 due to not/weak signal. Within the positive tumors, the mean percentage of tumor nuclei demonstrating ALK positivity was 58.5 (± 22.4). Patient's characteristics are summarized in Table 1. Among the 131 patients tested for ALK, mean age was 65,1 years (± 10,3), the majority were male (54.2%) and heavy smokers (50.4%), with a median of 69.2 packs/year. Half the patients were stage IV and the others stage I-III. About histologic characteristics, 125 patients (95.4%) had adenocarcinoma diagnosis, one was large cell carcinoma, one patient with mixed adenocarcinoma and the rest four with NOS (not otherwise specified) subtype. The most frequent procedure to obtain anatomo-pathological material was surgery (52.7%) and the most common location was primary tumor (74.8%). Clinico-pathological differences between ALK-positive and ALK-negative patients were analyzed. The mean age at the time of diagnosis for patients with ALK-positive was 56.6 years (± 18.2), compared with 65.6 years (± 9.5) for ALK-negative (p = 0.078). We observed a significant association between ALK translocation and never smoking habit (p = 0.004). Within the ALK positive patients, only one has NOS histology while the other seven were adenocarcinomas.
As mentioned before, ALK gene rearrangement analysis could not be performed by FISH technique in 28% (51/182) of cases (Table 2). The difficulties in obtaining adequate FISH tests were observed significantly more frequently for FNA (38.9% not evaluable, 7/18) and core-needle biopsy (38.7% not evaluable, 24/62) than for excisional and incisional biopsy (p = 0.009) (Fig. 2). Regarding the procedures, surgery was the most efficient obtaining only 12.7% (10/79) of not evaluable samples for FISH, while CT guided biopsy and TBB failed in 43.8% (21/48) and 41.3% (19/46) of patients respectively (p < 0.001) (Fig. 3).