Multiparametric molecular characterization of pulmonary sarcomatoid carcinoma reveals a nonrandom amplification of anaplastic lymphoma kinase (ALK) gene.

Background: Genetic alterations for targeting therapy are largely unexplored issues in pulmonary sarcomatoid carcinoma (PSC), a life-threatening tumor subset.

Methods: EGFR, HER2, KRAS, p53, CTNNB1, BRAF and PIK3CA mutations were assessed by direct sequencing, ALK, EGFR and HER2 gene status by fluorescence in situ hybridization (FISH), and ALK protein expression by immunohistochemistry (IHC) in 20 pleomorphic carcinomas (PLC), two pulmonary blastomas (PB) and one carcinosarcoma (CS). Surgical specimens and, in case of positivity, the corresponding preoperative biopsies were analyzed. Furthermore, 51 consecutive metastatic lung adenocarcinomas (MELAD) were used as controls for FISH and IHC assays of ALK gene.

Results: While no rearrangements of ALK were detected in PSC, relevant amplification was identified 5/23 (22%) surgical specimens and paired biopsies (four PLC and one PB, two females and three males, four current and one never smoker, aged 30-83 years). Considering tumor heterogeneity, the percentage of ALK amplified tumor cells ranged from 11% to 43%, with a mean gene copy gain (GCG ± SD) of 6.9 ± 0.8 and no signal differences between the epithelial (6.5 ± 0.9) and the sarcoma-like components (6.8 ± 0.9) of tumors. In the remaining 18 non-amplified PSC, the relevant value was 2.9 ± 0.5 in 1-80% tumor cells (p<0.001). ALK amplification was closely associated with chromosome 7 (EGFR) or 17 (HER2) polysomy (p<0.001). Out of 51 MELAD, 10 were ALK-rearranged (p=0.026) and only one amplified (p=0.009). No amplified tumors, either PSC or MELAD, expressed the relevant protein by IHC, while the 10 ALK-rearranged MELAD were strongly positive. TP53, KRAS and CTNNB1 mutations accounted for 30%, 22%, and 4% of cases, respectively, with no significant relationship with ALK amplification. No mutations for EGFR, HER2, BRAF or PIK3CA gene were observed.

Conclusion: ALK gene amplification is a nonrandom and clonally related event in a subset of PSC, but its biologic rationale deserves further investigation. KRAS mutation could represent a novel tool for therapy of such so deadly tumors with MEK inhibitors.