ALK-rearranged lung cancer in Chinese: a comprehensive assessment of clinicopathology, IHC, FISH and RT-PCR

Abstract

Approximately 3-7% of non-small cell lung cancers harbor an anaplastic lymphoma kinase (ALK) gene fusion, constituting a new molecular subtype of lung cancer that responds to crizotinib, an ALK inhibitor. Although previous studies have evaluated ALK-rearranged lung cancers, the comprehensive analysis of lung cancer in Chinese has not well assessed. Herein, we identified 44 cases of ALK-rearranged samples by fluorescent in-situ hybridization (FISH), immunohistochemistry (IHC), and reverse transcription polymerase chain reaction (RT-PCR) in a large number of surgically resected lung cancers. All 44 ALK-rearranged lung cancers were adenocarcinomas, with 2 cases having additional focal squamous components. The goal was to analyse the clinicopathological features of ALK-rearranged lung adenocarcinomas. Our data showed that a cribriform structure, prominent extracellular mucus and any type of mucous cell pattern may be either sensitive or specific to predict an ALK rearrangement. We used FISH as the standard detection method. We compared the ALK rearrangement accuracy of FISH, RT-PCR and IHC. RT-PCR could define both the ALK fusion partner and the fusion variant, but seemed unable to detect all translocations involving the ALK gene. It is noteworthy that IHC using the D5F3 antibody (Cell Signaling Technology) showed higher sensitivity and specificity than the ALK1 antibody (Dako). Therefore, we conclude that IHC remains a cost-effective and efficient technique for diagnosing ALK rearrangements and that D5F3 can be the optimal screening antibody in clinical practice.

Figure 1. Morphology of ALK-rearrangement lung adnenocarcinoma.

(A) papillary and micropapillary patterns; (B) mucinous cribriform pattern consisting of abundant extracellular mucus and cribriform structures; (C) solid pattern with signet ring cells; (D) mucinous cribriform pattern often floating within mucus-filled alveolar spaces; (E) mucous cells in form of goblet cells; (F) solid pattern with hepatoid tumor cells having abundant eosinophilic cytoplasm, round nuclei, and prominent nucleoli; the tumor cell nuclei are relatively monomorphic.

Figure 2. Two patterns of ALK gene alteration detected by FISH using Vysis LSI ALK Dual Color breakpoint probe.

(A) Two distinct red and green signals. (B) Isolated red signal.

Figure 3. Immunohistochemical staining with D5F3 and ALK1 detects ALK-rearrangement tumors.

Case 1: (A) score 3+ showing intense granular cytoplasmic staining with D5F3 antibody; (B) score 1+ showing faint cytoplasmic staining with ALK1; Case 2: (C) score 3+ showing intense granular cytoplasmic staining with D5F3; (D) score 2+ showing moderate, granular cytoplasmic staining with ALK1; Case 3: (E) score 3+ showing intense granular cytoplasmic staining with D5F3; (F) score 1+ showing faint, barely discernible cytoplasmic staining with ALK1.