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Q49. On immunophenotyping studies of chronic lymphocytic leukemias (CLL), the leukemic cells usually express antigens, 但通常不表現以下哪一個 markers?

  • (A) CD5
  • (B) CD20
  • (C) CD23
  • (D) FMC7
  • (E) Surface IgM
點此顯示正解

(D) FMC7

詳解

The question stem asks which marker CLL cells "usually do NOT express," meaning the question is looking for the FALSE/NEGATIVE marker.

Why (D) FMC7 is the Correct Answer

FMC7 is usually negative or absent in CLL, making it the marker that CLL cells do NOT express.1[^8] This is a defining characteristic of the CLL immunophenotype and is used in diagnostic scoring systems to distinguish CLL from other B-cell lymphoproliferative disorders.[^9] The absence of FMC7 expression (along with weak/absent CD79b) helps differentiate CLL from mantle cell lymphoma and other CD5+ B-cell malignancies.1[^8]

Why the Other Options Are Incorrect

(A) CD5 - POSITIVE in CLL. CLL cells characteristically co-express CD5 (normally a T-cell marker) along with B-cell antigens CD19, CD20, and CD23.123 This aberrant CD5 expression on B cells is a hallmark diagnostic feature of CLL.45

(B) CD20 - POSITIVE in CLL (though dim). CLL cells express CD20, but at characteristically lower intensity compared to normal B cells.123 This dim CD20 expression is part of the typical CLL immunophenotype.4[^11]

(C) CD23 - POSITIVE in CLL. CD23 expression is a key diagnostic marker for CLL.1235 The combination of CD5+/CD23+ double positivity has very high diagnostic value for distinguishing CLL from other B-cell malignancies, particularly mantle cell lymphoma (which is CD5+/CD23−).[9][12]

(E) Surface IgM - POSITIVE in CLL (though dim). CLL cells express surface immunoglobulin (IgM or IgD), but at characteristically low levels compared to normal B cells.123 This dim monoclonal surface immunoglobulin expression is part of the classic CLL immunophenotype.4[^11]

The typical CLL immunophenotype can be summarized as: CD5+, CD19+, CD23+, dim CD20, dim surface Ig, FMC7−, and weak/absent CD79b.14[^11]

詳解 · 中文翻譯

題目要求識別 CLL 細胞「通常不表現」的標誌，意思是題目尋找假陽性/陰性標誌。

為什麼 (D) FMC7 是正確答案

FMC7 在 CLL 中通常為陰性或缺失，使其成為 CLL 細胞不表現的標誌1[^8]。這是 CLL 免疫表型的定義特徵，用於診斷評分系統中區分 CLL 與其他 B 細胞淋巴增生性疾病[^9]。FMC7 表達的缺失（連同弱/缺失的 CD79b）有助於區分 CLL 與套細胞淋巴瘤和其他 CD5+ B 細胞惡性腫瘤1[^8]。

為什麼其他選項是不正確的

(A) CD5 - 在 CLL 中為陽性。CLL 細胞特徵性共同表達 CD5（通常是 T 細胞標誌）以及 B 細胞抗原 CD19、CD20 和 CD23123。B 細胞上這種異常的 CD5 表達是 CLL 的標誌性診斷特徵45。

(B) CD20 - 在 CLL 中為陽性（雖然表達強度弱）。CLL 細胞表達 CD20，但與正常 B 細胞相比表達強度特徵性較低123。這種弱 CD20 表達是典型 CLL 免疫表型的一部分4[^11]。

(C) CD23 - 在 CLL 中為陽性。CD23 表達是 CLL 的關鍵診斷標誌1235。CD5+/CD23+ 雙陽性的組合在區分 CLL 與其他 B 細胞惡性腫瘤（特別是套細胞淋巴瘤，其為 CD5+/CD23−）時具有很高的診斷價值[9][12]。

(E) 表面 IgM - 在 CLL 中為陽性（雖然表達強度弱）。CLL 細胞表達表面免疫球蛋白（IgM 或 IgD），但與正常 B 細胞相比水平特徵性偏低123。這種弱單克隆表面免疫球蛋白表達是典型 CLL 免疫表型的一部分4[^11]。

典型 CLL 免疫表型可總結為：CD5+、CD19+、CD23+、弱 CD20、弱表面 Ig、FMC7−、弱/缺失 CD79b14[^11]。

參考文獻 (AMA)

  1. Jain N, Wierda WG, O'Brien S. Chronic Lymphocytic Leukaemia. Lancet (London, England). 2024;404(10453):694-706. doi:10.1016/S0140-6736(24)00595-6. PMID:39068951. ↩↩↩↩↩↩↩↩↩↩↩↩↩↩

  2. Köhnke T, Wittmann VK, Bücklein VL, et al. Diagnosis of CLL Revisited: Increased Specificity by a Modified Five-Marker Scoring System Including CD200. British Journal of Haematology. 2017;179(3):480-487. doi:10.1111/bjh.14901. PMID:28832948. ↩↩↩↩↩↩↩↩

  3. Shadman M. Diagnosis and Treatment of Chronic Lymphocytic Leukemia: A Review. Jama. 2023;329(11):918-932. doi:10.1001/jama.2023.1946. PMID:36943212. ↩↩↩↩↩↩↩↩

  4. Salem DA, Stetler-Stevenson M. Clinical Flow-Cytometric Testing in Chronic Lymphocytic Leukemia. Methods in Molecular Biology (Clifton, N.J.). 2019;2032:311-321. doi:10.1007/978-1-4939-9650-6_17. PMID:31522426. ↩↩↩↩↩↩↩↩

  5. Hallek M. Chronic Lymphocytic Leukemia: 2020 Update on Diagnosis, Risk Stratification and Treatment. American Journal of Hematology. 2019;94(11):1266-1287. doi:10.1002/ajh.25595. PMID:31364186. ↩↩↩↩

  6. Hallek M. Chronic Lymphocytic Leukemia: 2025 Update on the Epidemiology, Pathogenesis, Diagnosis, and Therapy. American Journal of Hematology. 2025;100(3):450-480. doi:10.1002/ajh.27546. PMID:39871707. ↩

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