t(X;20)(q13;q13) is a very rare but recurrent translocation observed in myeloid neoplasms such as myelodysplastic neoplasm (MDS), myeloproliferative neoplasm (MPN), and acute myeloid leukemia (AML). While only nine cases have been reported previously,^1-5 we have collected data (including gene sequencing data) on a large series of 25 cases of myeloid neoplasms with t(X;20).

By retrospectively screening databases at 13 French cytogenetic laboratories, we identified 25 cases of t(X;20)(q13;q13) (Figure 1A,B; Table S1). The study was approved by the local institutional review board (AP-HP (Paris, France); reference: BPD2018DIA008) and complied with the tenets of the Declaration of Helsinki. All the patients provided their written, informed consent to participation. Bone marrow smears (available for 16 of the 25 patients) were blind-reviewed by two independent expert cytologists (J-FL and CS). To obtain R- or G-banded chromosomes, cells were prepared from bone marrow using standard techniques. All the karyotypes were reviewed by the members of the Groupe Francophone de Cytogénétique Hématologique and classified according to the International System for Human Cytogenetic Nomenclature (ISCN 2020). A complex karyotype was defined as the presence of three or more clonal chromosomal abnormalities (CAs). Standard fluorescence in situ hybridization was performed on metaphase and interphase nuclei, using the commercial probes XIST (Xq13.2)/CCPX (CytoTest, Rockville, MD, USA), 20q12 (PTPRT)/20q13 (MYBL2) (Cytocell, Cambridge, UK), WCP20 and WCPX (Metasystems, Altlußheim, Germany). Fourteen patient samples were sequenced with a next-generation sequencing myeloid panel (Supplemental Information).

For one center (Pitié-Salpêtrière, between 2015 and 2022), we were able to calculate the exact prevalence of t(X;20) in MDS (0.4%; 2 out of 421) and in MDS or unexplained cytopenia (0.1%; 2 out of 1283). All 25 patients were female. The median age was 78 (range: 60–91). Five of the 23 patients with available clinical data had received chemotherapy for follicular lymphoma (case #1), multiple myeloma (case #16), breast cancer (case #19), ovarian cancer (case #14) or AML (case #24) before the t(X;20) was detected.

The initial diagnoses were MDS (n = 12, including ring sideroblasts in cases #2, #8, and #18), cytopenia (n = 6), AML (n = 3), and MPN with eosinophilia (n = 1). Three myelograms were hemodiluted so a morphologic diagnosis could not be made. The morphologic review of 16 samples confirmed the diagnoses for 11 cases of MDS and one case of AML and led to the reclassification of two out of four cases of cytopenia as unclassifiable MDS (MDS-U, cases #6 and #21) (Figure S1). The two reviewers observed an abnormal chromatin clumping in 6/16 (37%) cases, but no specific feature of the t(X;20). Finally, the four remaining cases of cytopenia were considered to be clonal cytopenia of undetermined significance (CCUS).

In the 14 cases of MDS and 4 cases of CCUS, the karyotype was never complex; the t(X;20) was the only CA in 12 of the 18 cases (67%). In the other 6 cases, the additional CAs were del(5q) (3 out of 18, 17%; none in CCUS), del(20q) (2 out of 18, 11%; none in CCUS), and trisomy (tri) 8 (1 out of 18, 5%). The t(X;20) was subclonal in only one of the 18 cases (5%). In cases presenting with both t(X;20) and del(20q), the two CAs were always in independent clones. All the cases of AML had complex karyotypes with 3 to 7 CAs. The t(X;20) was present in the major clone in all three patients (Tables S1 and S2).

In the cohort as a whole, the most common associated CA was del(5q) (6 out of 25, 24%)—which was variously clonal, subclonal, or present in independent clones—and followed by del(20q) (3 out of 25, 12%) or tri8 (2/25, 8%). It is noteworthy that in one patient (case #24), tri8 was present in 24 of the 25 (96%) mitoses observed at the time of AML diagnosis. Four months later (during the first-line treatment), tri8 was still observed in three mitoses independently of t(X;20); this might correspond to residual AML blasts. At relapse 2 years later, tri8 reappeared (additionally with tetrasomy 8), whereas t(X;20) was no longer observed (Figure S2). In all 14 tested cases, the breakpoint on the X chromosome was proximal to XIST (Xq13.2), and the breakpoint on chromosome 20 was distal to MYBL2 on 20q13 (Figure 1C,D). Molecular data revealed mutations in TET2 (n = 7 out of 14, 50%), SF3B1 (n = 3, 21%), DNMT3A (n = 3, 21%), RUNX1 (n = 2, 14%), and U2AF1 (n = 2, 14%) (Table S1). Of note, the 3 patients with SF3B1mut also had a del(5q); and the only CCUS case tested by NGS had mutations in TET2 and DNMT3A. No TP53 mutations were observed. We also detected mutations in SRSF2, BCOR, BCORL1, IDH1, EP300, NRAS, and ETV6 (n = 1 each).

Regarding MDS and CCUS, the cytogenetic category for the Revised International Prognostic Scoring System (IPSS-R) score was intermediate in all but the three cases of MDS with t(X;20) and del(5q) (with a favorable score).⁶ The median MDS IPSS-R score was 2.25 (range, 1–4). Of the 18 scores, 15 (83%) were classified as low risk, one was classified as very low risk, and two were classified as intermediate risk (Table S1 and Figure 1E). With a median follow-up time of 17 months (95% CI: 10–37), the median overall survival was not reached, and 69% of the patients were alive at 5 years.

To the best of our knowledge, the present series of t(X;20) cases is the largest yet. As previously described, all patients were female, and the median age was 78. The majority (64%) of t(X;20) cases corresponded to MDS. The morphological evidence for MDS was not always easy to interpret: two of the four morphologically reviewed cases of cytopenia were reclassified as MDS. However, four cases of cytopenia had no morphological evidence of MDS. According to the fourth edition of the World Health Organization's classification of hematolymphoid tumors, t(X;20)(q13;q13) is not one of the CAs that defines MDS-U. In the fifth edition, patients with isolated t(X;20)(q13;q13) are classified as having CCUS. In our series of MDS/CCUS cases, t(X;20) was frequently isolated (in 67% of cases) and was associated with a low-risk MDS IPSS-R in 83% of cases. Overall, t(X;20) was associated with cases of MDS/CCUS (82%) with a favorable prognosis. In a few cases, t(X;20) was observed in AML but only included in a complex karyotype. Our series included a case of MPN with hypereosinophilia. t(X;20) was frequently isolated or present in the major clone, and may be an early event. The most frequent associated CA was del(5q) (24%). Interestingly, when associated with del(20q) (12%), t(X;20) was always present in an independent clone. This is in line with the possible silencing of 20q genes by a position effect of the XIST gene on der(20).² The spreading of X inactivation to the 20q region provides an alternate mechanism for del(20q).⁴ Indeed, in all the tested cases, XIST gene was translocated on the der(20), and all 20q genes stayed on the long arm of der(20).

In conclusion, t(X;20)(q13;q13) is a rare translocation observed in older women. It may be an early event. t(X;20)(q13;q13) is often isolated and is mostly associated with MDS/CCUS with a favorable prognosis. It is found less frequently in cases of AML and MPN. The most commonly associated CAs are del(5q) and del(20q), and the latter is always in an independent clone. We therefore suggest that isolated t(X;20) should be classified in a good cytogenetic IPSS-R category (score = 1), rather than in an intermediate cytogenetic category (score = 2).

t(X;20)(q13;q13) 是一种非常罕见但反复发生的易位，在骨髓增生异常肿瘤 (MDS)、骨髓增生性肿瘤 (MPN) 和急性髓系白血病 (AML) 等髓系肿瘤中观察到。虽然之前只报道了 9 例病例，但我们已经收集了 25 例 t(X;20) 骨髓肿瘤病例的大系列数据（包括基因测序数据）^{1-5 。}

通过回顾性筛选法国 13 个细胞遗传学实验室的数据库，我们发现了 25 例 t(X;20)(q13;q13) 病例（图 1A、B；表 S1）。该研究得到了当地机构审查委员会（AP-HP（法国巴黎）；参考号：BPD2018DIA008）的批准，并符合赫尔辛基宣言的原则。所有患者都提供了参与的书面知情同意书。骨髓涂片（适用于 25 名患者中的 16 名）由两名独立的细胞专家专家（J-FL 和 CS）进行盲审。为了获得 R 或 G 带染色体，使用标准技术从骨髓中制备细胞。所有核型均由法语细胞遗传学血液组成员进行审查，并根据国际人类细胞遗传学命名系统 (ISCN 2020) 进行分类。复杂核型被定义为存在三个或更多克隆染色体异常（CA）。使用商业探针 XIST (Xq13.2)/CCPX (CytoTest, Rockville, MD, USA)、20q12 (PTPRT)/20q13 (MYBL2) (Cytocell, Cambridge, UK) 对中期和间期细胞核进行标准荧光原位杂交）、WCP20 和 WCPX（Metasystems，德国 Altlußheim）。使用下一代测序骨髓组对 14 名患者样本进行了测序（补充信息）。

对于一个中心（Pitié-Salpêtrière，2015 年至 2022 年），我们能够计算出 t(X;20) 在 MDS 中的准确患病率（0.4%；421 例中有 2 例）和 MDS 或不明原因血细胞减少症（0.1%；2 例）中的确切患病率。 1283 中的 2）。所有 25 名患者均为女性。中位年龄为 78 岁（范围：60-91 岁）。拥有可用临床数据的 23 名患者中有 5 名接受过针对滤泡性淋巴瘤（病例#1）、多发性骨髓瘤（病例#16）、乳腺癌（病例#19）、卵巢癌（病例#14）或 AML（病例#24）的化疗。 ) 在检测到 t(X;20) 之前。

最初诊断为 MDS（n  = 12，包括病例 #2、#8 和 #18 中的环形铁粒幼细胞）、血细胞减少症（n  = 6）、AML（n  = 3）和伴嗜酸性粒细胞增多的 MPN（n  = 1）。三份骨髓造影经过血液稀释，因此无法做出形态学诊断。对 16 个样本的形态学检查证实了 11 例 MDS 和 1 例 AML 的诊断，并将四分之二的血细胞减少病例重新分类为无法分类的 MDS（MDS-U，病例 #6 和 #21）（图 S1） ）。两位评审员在 6/16 (37%) 病例中观察到异常染色质聚集，但没有 t(X;20) 的具体特征。最后，其余四例血细胞减少症被认为是意义未定的克隆性血细胞减少症（CCUS）。

14例MDS和4例CCUS的核型并不复杂； t(X;20) 是 18 例中有 12 例 (67%) 中唯一的 CA。在其他 6 例中，额外的 CA 为 del(5q)（18 例中有 3 例，17%；CCUS 中无）、del(20q)（18 例中有 2 例，11%；CCUS 中无）和三体性（三体） ) 8（18 人中有 1 人，5%）。 18 例中仅 1 例 (5%) 的 t(X;20) 为亚克隆。在同时出现 t(X;20) 和 del(20q) 的病例中，两个 CA 始终处于独立克隆中。所有AML病例均具有复杂的核型，有3至7个CA。 t(X;20) 存在于所有三名患者的主要克隆中（表 S1 和 S2）。

在整个队列中，最常见的相关 CA 是 del(5q)（25 例中的 6 例，24%）——它是不同的克隆、亚克隆或存在于独立克隆中——其次是 del(20q)（25 例中有 3 例） 25, 12%) 或 tri8 (2/25, 8%)。值得注意的是，在一名患者（病例#24）中，在 AML 诊断时观察到的 25 个有丝分裂中有 24 个（96%）有 tri8 存在。四个月后（一线治疗期间），在三个有丝分裂中仍观察到 tri8，与 t(X;20) 无关；这可能对应于残留的 AML 原始细胞。两年后复发时，tri8 再次出现（另外还有 8 号四体），而不再观察到 t(X;20)（图 S2）。在所有 14 个测试病例中，X 染色体上的断点靠近XIST (Xq13.2)，20 号染色体上的断点位于20q13 上的MYBL2远端（图 1C、D）。分子数据显示TET2（ 14 例中有 7 例，50%）、SF3B1 （ n =  3，21%）、DNMT3A（n  = 3，21%）、RUNX1（n  = 2，14%）和U2AF1存在突变( n  = 2, 14%)（表 S1）。值得注意的是，3 名SF3B1 mut患者也有 del(5q)；唯一经NGS检测的CCUS病例存在TET2和DNMT3A突变。没有观察到TP53突变。我们还检测到SRSF2、BCOR、BCORL1、IDH1、EP300、NRAS和ETV6中的突变（各n  = 1）。

关于 MDS 和 CCUS，除了 t(X;20) 和 del(5q) 的 3 例 MDS 病例（得分良好）外，修订后的国际预后评分系统 (IPSS-R) 评分的细胞遗传学类别均处于中等水平。⁶ MDS IPSS-R 评分中位数为 2.25（范围：1-4）。在 18 个评分中，15 个（83%）被分类为低风险，1 个被分类为极低风险，2 个被分类为中风险（表 S1 和图 1E）。中位随访时间为 17 个月（95% CI：10-37），但未达到中位总生存期，69% 的患者在 5 岁时仍存活。

据我们所知，目前的 t(X;20) 系列案件是迄今为止规模最大的。如前所述，所有患者均为女性，中位年龄为 78 岁。t(X;20) 病例中的大多数 (64%) 对应于 MDS。 MDS 的形态学证据并不总是容易解释：四个形态学审查的血细胞减少病例中有两个被重新分类为 MDS。然而，4 例血细胞减少症没有 MDS 的形态学证据。根据世界卫生组织第四版血淋巴肿瘤分类，t(X;20)(q13;q13)不是定义MDS-U的CA之一。在第五版中，孤立的 t(X;20)(q13;q13) 患者被归类为患有 CCUS。在我们的 MDS/CCUS 病例系列中，t(X;20) 经常被孤立（67% 的病例），并且在 83% 的病例中与低风险 MDS IPSS-R 相关。总体而言，t(X;20) 与预后良好的 MDS/CCUS 病例 (82%) 相关。在少数情况下，在 AML 中观察到 t(X;20)，但仅包含在复杂核型中。我们的系列包括一例伴有嗜酸性粒细胞增多的 MPN 病例。 t(X;20) 经常被分离或存在于主要克隆中，并且可能是早期事件。最常见的相关 CA 是 del(5q) (24%)。有趣的是，当与 del(20q) (12%) 相关时，t(X;20) 始终存在于独立克隆中。这与XIST基因对 der(20)的位置效应可能导致的 20q 基因沉默一致。 ² X 失活扩散到 20q 区域为 del(20q) 提供了另一种机制。⁴事实上，在所有测试的病例中，XIST基因易位到 der(20) 上，所有 20q 基因都保留在 der(20) 的长臂上。

总之，t(X;20)(q13;q13) 是老年女性中观察到的罕见易位。这可能是一个早期事件。 t(X;20)(q13;q13) 通常是孤立的，并且大多与预后良好的 MDS/CCUS 相关。在 AML 和 MPN 病例中较少见。最常见的关联 CA 是 del(5q) 和 del(20q)，后者始终位于独立克隆中。因此，我们建议分离的 t(X;20) 应归入良好的细胞遗传学 IPSS-R 类别（分数 = 1），而不是归入中间细胞遗传学类别（分数 = 2）。