Significance Of ALK Gene Translocation And ALK Fusion Protein Detection In Anaplastic Large Cell Lymphoma

Backgrounds and aimsAnaplastic large cell lymphoma(ALCL) represents a distinct category of large cell lymphomas defined by a strong expression of the cytokine receptor CD30 on neoplastic cells and a so-called anaplastic cytology.Anaplastic large cell lymphoma kinase(ALK) is a specific molecular marker in ALCL.According to the survey,In 60%-85%of ALCL cases the expression of ALK fusion protein could be detected. The expression of the chimeric protein is caused by the translocation between chromosome 2 and 5,et al.All these translocations involve the ALK gene located in chromosome 2 and create a new fusion ALK gene.ALK(+) ALCL appears to benefit from chemotherapy more than ALK(-) forms of systemic ALCL.So It is necessary to detect the ALCL with ALK fusion gene or not.In this study 30 cases of ALCL were analyzed in order to observe their clinicopathologic,immunophenotypic and molecular biological features,especially the ALK fusion gene and protein levels by using fluorescence in situ hybridization(FISH),immunohistochemistry and T cell receptor(TCR)βandγgene rearrangement in Paraffin-Embedded Tissues of ALCL. Tissue microarray technique was used for compareing the value of FISH with that of immunohistochemistry in detecting ALK gene translocations and ALK fusion protein in ALCL.Meanwhile,the relation of the ALK gene translocation,ALK fusion protein and prognostic in ALCL was also observed. Methods30 cases of ALCL,including 28 cases of systemic ALCL and 2 cases of primary cutaneous ALCL were collected from the pathology department of Nanfang Hospital and Fuzhou general Hospital of PLA.The histopathological classification used in this study was new WHO classification(2001).Tissue microarray technique was used to construct a tissue chip with 96 spots containing 2 cases of normal tissues as control group,30 cases of ALCL tissues.Paraffin blocks of these cases were cut for immunostaining.SP method was used for immunostaining and the first antibodies were CD3,CD20,CD45RO,CD79a,CD30 and ALK.Dual-color FISH and immunohistochemistry were used to detect ALK gene translocation and ALK fusion protein.Results1.Histopathologically,there were 22 cases of common variant(78.6%),4 of lymphohistocytic variant(14.3%),2 of small cell variant(7.1%) in 28 systemic cases, and 2 cases of primary cutaneous ALCL.and2.Immunohistochemically,29 cases(29/30,96.7%) were CD30 strong positive. In which 23 cases(23/30,76.7%) with CD3 and/or CD45RO positivity,whereas 7 cases(7/30,23.3%) without CD3,CD45RO,CD20 and CD79a positivities.ALK was detected in 20 of 28 systemic ALCLs(71.4%,20/28) in which 16 cases of common variant(72.7%,16/22):3 cases of lymphohistocytic variant(75%,3/4) and I cases of small cell variant.In 20 cases,ALK were expressed with nuclear and cytoplasmic positive products.The positive rate of ALK has no significant difference between variants(P＞0.05).In the two cases of primary cutaneous ALCL,there was negative reaction for ALK.3.In 28 systemic cases,The detection rates of TCR-γchain gene rearrange -ments was 71.4%(20/28);The detection rates of TCR-βchain gene rearrangements was 46.4%(13/28).There were 11 cases(11/28,39.3%) with TCR-γand TCR-βchain gene rearrangement.2 cases of primary cutaneous ALCL harbors TCR-γand TCR-βgene rearrangement.4.ALK gene translocation was found in 17 of 28 cases(17/28,60.7%) of systemic ALCL by FISH.Meanwhile,there wasn't ALK fusion protein being found in two cases of primary cutaneous ALCL.5.Clinically,ALCLs without ALK gene aberrations were much older than those with this abnormalities(P=0.003).The survival rate of patients with ALK gene aberrations was%,whereas%of the patients without ALK gene abnormalities. Survival curves of these two groups showed a statistic significant distinguishability (P=0.0018).Conclusion1.It is significative to distinguish the ALCL with ALK fusion gene from ALCL without ALK fusion gene because of clinical diagnosis and prognostic.2.The three methods to detecting ALK fusion gene or its product show different specificity and sensitivity.With its simplicity,rapid and low cost,immunohistochem -ical method is the first choice in detecting ALK gene translocation,but FISH is specific valuable for the diagnosis of ALCL.When conditions permit,FISH can be the first choice for its accur.3.As we know,this is the first investigation of the relation of the ALK protein, age and prognostic in ALCL by tissue microarray technique up to now.4.In this study,ALK fusion gene and ALK fusion protein shows a high incidence rate in ALCL especially in low age group.So it should become an important and independent marker for clinical diagnosis and prognosis estimation of ALCL.