The Role And Significance Of ALK Gene In Surgical Pathology Diagnosis

BackgroundAnaplastic lymphoma kinase-ALK gene is located on the short arm of chromosome 2 and encodes a receptor tyrosine kinase(RTK),which is a member of the insulin receptor family.Since the first discovery of the ALK-NPM fusion gene caused by the rearrangement of chromosomes 2 and 5 in Anaplastic Large Cell lymphoma,the structure of ALK gene,mutation patterns,associated tumors,and vast studies had been performed on target therapies.It has been found that the structure of ALK gene includes three major components: the extracellular binding domain,the transmembrane domain and the intracellular kinase domain.The binding domain binds to the ligand and plays its key role through the kinase domain.Mutations of ALK gene have been found in a variety of tumors.Mutation patterns include fusion,which is the most common type,and point mutation and amplification,which are less common.The typical ones include NPM-ALK fusion common in anaplastic large cell lymphomas(ALCLs),ALK-EML4 fusion common in non-small cell lung cancers(NSCLCs),TPM3-ALK and TPM4-ALK fusion in inflammatory myofibroblastic tumors(IMTs),ALK F1174 L mutations in neuroblastomas(NBs),and other fusions occasionally reported in kidney,colon,breast,thyroid,esophageal,and ovarian cancers.Mutations of ALK genes are involved in the pathogenesis and development of tumors,and the study of the fusion gene domain is helpful to understand the mechanism of its action.Some fusion genes,such as NPM-ALK,have been certain understood of the structure and mechanism of action,but the specific mechanism of the involvement of most fusion genes in the pathogenesis is not yet clear.Aimed at ALK molecular targeted therapy,such as ALK inhibitors crizotinib and ceritinib has greatly improved the prognosis of patients,but such drugs are prone to drug resistance,a number of studies have shown that drug mediated second mutation is involved in the formation of the resistance,but the specific mechanism has not been fully elucidated,the development of new drug still has great difficulties.AimsTo investigate the role and significance of ALK mutation in anaplastic large cell lymphomas,inflammatory myofibroblastic tumors,non-small cell lung cancers,histiocytosis,and other tumors.MethodsIn this study,839 cases were selected from the case bank of the Second Affiliated Hospital of Guangzhou Medical University and consultation cases from2010 to 2021.Clinical data of 8 cases of anaplastic large cell lymphomas,8 cases of inflammatory myofibroblastic tumors,818 cases of non-small cell lung cancers,3cases of ALK-positive histiocytosis,1 case of ALK+ large B cell lymphoma and 1case of neuroblastoma were collected.Routine hematoxylin-eosin staining was used to observe the histopathological characteristics of the cases.The expression level of ALK protein was detected by immunohistochemistry.The mutation of ALK gene was detected by fluorescence in situ hybridization(FISH)and Next-generation sequencing(NGS).Results1.Clinical features: There were 8 ALCL patients,median age was 23.5 years old,and the male to female ratio was 3:1.Most of the clinical symptoms were lymph node enlargement accompanied by fever.The median age of 6 typical IMTs was 43 years old,and the male-to-female ratio was 1:1.The lesions were located in the breast,liver,lung and vulva.Two cases of epithelioid inflammatory myofibroblastic sarcoma(EIMS)occurred in a woman aged 26 years old and a man aged 47 years old.There were 818 cases of non-small cell lung cancers(NSCLCs),the median age of onset was 63 years old,and the male to female ratio was 1.7:1.Of these,46 cases were ALK-positive with a median age of 57 years old and a male-to-female ratio of1.26 to 1.Three cases of ALK-positive histiocytosis were reported in a 20-year-old male presenting with nasal polyps,a 32-year-old woman presenting with a mass in the foramen,and a 28-year-old woman presenting with a mass in the left leg.A case of ALK-positive large B-cell lymphoma in an 8-year-old boy presenting with humerus mass.A case of neuroblastoma in a 3-year-old girl with mass in frontal lobe.2.Pathological features: All the 8 cases showed typical features under the microscope.There were 6 typical IMTs and 2 EIMS cases with marked atypia cells.Of the 818 NSCLCs,627 were adenocarcinomas and 191 were squamous cell carcinomas,while 43 adenocarcinomas and 3 squamous cell carcinomas were ALKpositive.28/43(65%)were poorly differentiated adenocarcinomas,accounting for the majority.Squamous cell carcinomas are relatively rare,mainly medium or poorly differentiated squamous cell carcinomas.The lymph node metastasis rate of ALKpositive was higher than that of ALK-negative.Epithelioid histiocytic morphology,xanthomatous morphology and spindle cell morphology were seen in ALK-positive histiocytosis.Cell atypia was not obvious in all cases.1 case of ALK-positive LBCL showed diffuse growth pattern with plasmablastic differentiation.1 case of neuroblastoma showed patchy small cell proliferation with obvious atypia,the background was neuropil.3.Immunophenotype and molecular characteristics: ALK-positive ALCL was found in 5 of the 8 ALCLs(62.5%)by IHC,and ALK split was confirmed in 3 of them by FISH.ALK-positive IMTs was found in 4 of the 8 IMTs(50%)by IHC,of which ALK split was confirmed by FISH in 2 typical IMTs,and RANBP2-ALK and EML4-ALK fusion were confirmed in 2 EIMS cases respectively by FISH and NGS.ALK gene mutation was detected in 29 of the 46 ALK-positive NSCLC cases by fluorescence in situ hybridization,and 26 of them were positive,including 24 adenocarcinomas and 2 squamous cell carcinomas.KIF5B-ALK fusion had been detected in 3 cases of ALK-positive histiocytosis by FISH and NGS.ALK immunohistochemistry showed strong staining in 1 LBCL and 1 NB.Conclusions1.The positive rate of ALK in ALCL was 62.5%,and ALK mutations were common in younger patients in ALCL,but there was no significant correlation between morphology and ALK mutations.2.The positive rate of ALK in IMT was 50%,while pulmonary EIMS may be associated with rare EML4-ALK fusion,which suggests a poor prognosis.3.The positive rate of ALK in NSCLC was 5.6%,ALK mutations were generally found in adenocarcinomas,most common in poorly differentiated adenocarcinomas,and may be accompanied by mucinous differentiation or signet-ring cell components;ALK-postive NSCLCs were prone to lymph node metastasis,but there was no statistical significance between ALK+ and ALK-.4.Some of the tumors associated with ALK,such as LBCLs,are very aggressive.In contrast,ALK-postive histiocytosis has an excellent prognosis.