伴不典型BCR-ABL融合基因的慢性髓性白血病的临床和实验研究

A clinical and laboratory study of chronic myeloid leukemia with atypical BCR-ABL fusion gene subtypes

目的探讨伴不典型BCR-ABL融合基因亚型e14a3和e19a2型慢性髓性白血病（cML）的临床和实验室特点。方法对2004至2012年染色体核型分析有t（9；22）（q34；q11），荧光原位杂交（FISH）证实为BCR-ABL融合基因阳性，而常规实时定量PCR（RQ．PCR）检测常见BCR—ABL融合基因（b3a2、b2a2和ela2）阴性的6例CML患者，重新设计引物进行PCR扩增，并将扩增产物测序，以明确不典型BCR-ABL融合基因类型。对BCR．ABL融合基因扩增产物进行突变检测。对患者的临床资料进行回顾性分析。结果6例患者PCR扩增产物经测序分析，其中5例为e14a3型，1例为e19a2型。5例e14a3型CML患者中，男4例，女1例，中位年龄48岁，慢性期4例，加速期1例；1例e19a2型患者为女性，40岁，CML慢性期，PLT〉1000×10^9／L。5例e14a3型CML患者中4例在羟基脲或IFN治疗无效后予以伊马替尼（IM）治疗，1例行造血干细胞移植（HSCT）。前4例患者中1例因有E255K突变而对IM耐药，改用达沙替尼后获完全细胞遗传学反应（CCyR）；1例在IM治疗获CCyR后3个月复发并急变，最终死亡；2例IM治疗后获CCyP．目前状态稳定，仍处于CCyR，尽管其中1例伴有1293T突变。行HSCT治疗患者目前处于CCyR。1例e19a2型CML患者羟基脲治疗后获得完全血液学反应，后改用IM治疗，很快获得CCyR。结论伴不典型BCR-ABL融合基因的CML发病率极低，酪氨酸激酶抑制剂或HSCT都可以取得疗效，常规RQ-PCR可能漏检少见的不典型BCR-ABL融合基因亚型。

Objective To explore the clinical and laboratory features of chronic myeloid leukemia （CML） with atypical e14a3 and e19a2 BCR-ABL fusion gene subtypes. Methods We retrospectively analyzed a cohort of CML patients with Ph chromosome positive confirmed by cytogenetic and FISH but classical e13a3 （b2a2）, e14a2 （b3a2） and ela2 fusion transcripts negative identified by conventional real- time quantification RT-PCR （RQ-PCR）. Further RQ-PCR was done with the forward primer and reverse primer designed to detect rare atypical BCR-ABL fusion genes including e14a3 and e19a2 transcripts. Direct sequencing analysis was performed on the PCR products and mutations in the BCR-ABL kinase domain were detected. The clinical data of patients were retrospectively analyzed. Results Six CML patients were found to carry t （9;22） abnormality and BCR-ABL rearrangement confirmed by FISH but classical BCR-ABL fusion genes negative detected by RQ-PCR. Further RQ-PCR and sequencing analysis confirmed the fusion of BCR exon 14 and ABL exon 3 in five CML patients （casel-5） and the fusion of BCR exon 19 and ABL exon 2 in one CML patient （case 6）. E255K and I293T IM-resistant mutations were detected in case 1 and 2, respectively. Among five cases with e14a3 transcripts, four were CML-CP, one CML-AP. Four patients were male and one was female. The median age was 48 years. The patient （case 6） with e19a2 transcripts was 40-year-old female with a diagnosis of CML-CP and PLT count was more than 1 000x 109/L. Imatinib （IM） therapy was administed in case 1, 2, 3, 4 and hematopoietic stem cell transplantation （HSCT） was undergone in case 5 after hydroxyurea （Hu） or interferon failure. Case 1 who had E255K IM resistant mutation, responded poorly to IM but obtained a complete cytogenetic remission （CCyR） after a substitution of dasatinib for IM. Case 2 and 3 achieved CCyR 6 months later after IM treatment and had been maintained well with IM despite I293T mutation in case 2. Case 4 attained CCyR 3 months later after IM treatment but relapsed and died soon. Case 5 was still in CCyR after HSCT. Case 6 with e19a2 transcripts got complete hematologic response after Hu treatment and CCyR was achieved soon after IM therapy. Conclusion Incidence of CML with atypical transcripts is extremely low. They could benefit from tyrosine kinase inhibitors or HSCT. Rare and atypical BCR-ABL fusion gene subtypes could be missed by conventional RQ-PCR.