背景：

子宫下段（lower uterine segment）作为子宫的一部分，位于宫颈及子宫体之间，该处发生的子宫内膜癌具有独特的临床病理特征。多项研究表明，相较于常见的子宫体子宫内膜癌，子宫下段内膜癌（Lower uterine segment cancer，LUSC）与深肌层浸润和淋巴结转移率高等高危临床病理特征相关。并且，LUSC患者中林奇综合征的检出率远高于子宫体子宫内膜癌患者。随着测序技术的发展，子宫内膜癌分子分型对患者的预后评估及辅助治疗选择十分重要。然而，目前少有关于LUSC分子分型特征谱的系统研究，其分子分型的分布特点及其对预后的影响尚未阐明。本研究通过单中心回顾性分析，系统探讨LUSC的分子分型特征及其与临床病理特点的相关性，旨在为这一特殊亚型子宫内膜癌患者的个体化诊疗提供理论依据。

方法：

回顾性收集2016年3月至2023年11月北京协和医院收治的62例LUSC患者的临床病理资料。在确保标本质量的前提下，对其中符合进一步测序条件的54例石蜡标本进行分子检测，提取石蜡样本DNA行二代测序检测，并同时采用免疫组化染色方法行错配修复蛋白（MLH1、PMS2、MSH2、MSH6）、p53蛋白、ER、PR染色。评估并分析LUSC患者的分子分型与组织学类型、组织学亚型、临床预后等临床病理特征之间的相关性，并描述其在不同版本国际妇产科联盟（International Federation of Gynecology and Obstetrics ，FIGO）分期以及预后风险分级中的变化。

结果：

（1）共纳入62例LUSC患者，平均年龄49岁，80.6%初诊时有临床症状（以不规则阴道流血、绝经后出血为主）。组织学以子宫内膜样癌（75.8%）为主，43.5%为侵袭性亚型。43.5%肿瘤浸润超过1/2子宫肌层，24.2%存在淋巴血管间隙侵犯（lymph vascular space invasion，LVSI），17.7%发生淋巴结转移。免疫组化显示ER和PR的阳性率分别为77.4%和69.4%。根据FIGO分期（2009版），FIGO I期30例（48.4%），II期13例（21.0%），III期18例（29.0%），IV期1例（1.6%）。

（2）54例LUSC患者完成二代测序以及免疫组化染色并行分子分型，结果显示：POLE超突变（POLE ultra-mutated，POLE mut）型6例（11.1%），错配修复缺陷（Mismatch repair deficiency，MMRd）型14例（25.9%），p53异常（p53 abnormality，p53 abn）型9例（16.7%），无特殊分子改变（Non-specific molecular profile，NSMP）型25例（46.3%）。其中2例（3.7%）具有多重分子特征（1例POLE mut+p53 abn，1例MMRd+p53 abn）。

（3）6例POLE mut LUSC患者平均发病年龄47岁，均以异常阴道出血就诊。其中5例为子宫内膜样癌（EEC），以低分化为主(4/5），但均无LVSI或淋巴结转移；14例MMRd型LUSC患者平均发病年龄45岁，组织学以子宫内膜样癌为主（11/14，78.6%），高-中分化EEC 9例（81.8%）。MMR蛋白缺失以MSH2+MSH6共缺失（50%）和MLH1+PMS2共缺失（35.7%）为主；9例p53 abn型LUSC患者平均发病年龄55岁，5例为EEC，以高至中分化为主（4/5）。存在深肌层浸润（≥1/2）6例（66.7%），LVSI 4例（44.4%）和淋巴结转移1例（11.1%）。25例NSMP型平均发病年龄49岁，组织学大部分为EEC（20/25，80%），侵袭性组织学亚型8例（32.0%）。深肌层浸润9例（36.0%）和淋巴结转移2例（8.0%）。

（4）LUSC各分子分型间，子宫内膜样癌病理学分级（P=0.037）和FIGO分期（纳入分子分型的2023版）（P=0.004）差异具有统计学意义。POLE mut型子宫内膜样癌中，高级别EEC占比更高；MMRd型、p53 abn和NSMP型EEC中，低级别EEC更常见。

（5）54例LUSC患者根据FIGO分期（2009版）和FIGO分期（2023版）标准进行分期，变化主要集中于Ⅰ、Ⅱ期病例（12/54，22.2%），而Ⅲ、Ⅳ期患者的分期结果未发生变动。新版中10例患者分期上调由Ⅰ期上调至Ⅱ期，2例由Ⅱ期降期为Ⅰ期。生存分析结果显示，不同FIGO分期标准中患者的PFS、OS均具有统计学意义（P<0.0001），Ⅰ期预后最好，其次是Ⅱ期、Ⅲ期，Ⅳ期预后最差。

（6）54例LUSC患者根据未知分子分型的预后风险分级标准，低危13例（24.1%），中危5例（9.3%），高-中危14例（25.9%），高危21例（38.9%），进展转移1例（1.9%）。根据已知分子分型的预后风险分级标准，低危17例（31.5%），中危4例（7.4%），高-中危7例（13.0%），高危18例（33.3%），进展转移1例（1.9%）。其中，5例患者为风险降级，另有5例患者为风险升级。

结论：

本研究基于免疫组化与二代测序技术，对54例中国LUSC患者进行了系统的分子分型分析，是目前国内样本量最大的相关研究。结果显示，子宫下段内膜癌作为一种罕见且独特的子宫内膜癌亚型，发病年龄更加年轻，组织学分级更高，深肌层浸润（≥1/2肌层）的发生率更高，更易发生淋巴结转移，中晚期患者比例较高。尽管LUSC的分型模式与UCEC类似，但在各分型所对应的临床病理特征上存在差异。LUSC中NSMP型患者呈现出更高的临床风险，p53 abn型具有复杂的生物学行为，MMRd型中MSH2和MSH6缺失比例较高，提示其可能具有更高的林奇综合征相关性，而POLE mut型则与UCEC具有相似的病理特征。以上发现不仅加深了对LUSC生物学特征的认识，也为其分层管理与个体化治疗提供了理论依据。

Background:

The lower uterine segment (LUS), as an anatomical region between the cervix and the uterine corpus, gives rise to endometrial carcinomas with distinct clinicopathological characteristics. Multiple studies have demonstrated that, compared to conventional uterine corpus endometrial carcinomas, Lower uterine segment cancer (LUSC) was associated with high-risk pathological features, including myometrial infiltration more than 1/2 and a higher rate of lymph node metastasis. Moreover, the prevalence of Lynch syndrome is significantly higher in LUSC patients than in those with uterine corpus of endometrial carcinoma. With advances in sequencing technologies, molecular classification has become crucial for prognostic stratification and adjuvant therapy decision-making in endometrial carcinoma. However, systematic investigations into the molecular profiling of LUSC remain scarce, and the distribution patterns of molecular subtypes and their prognostic implications have yet to be elucidated. This study conducts a single-center retrospective analysis to comprehensively explore the molecular characteristics of LUSC and their correlations with clinicopathological features. The findings aim to provide a theoretical foundation for the personalized management of this unique endometrial carcinoma subtype.

Methods

A retrospective analysis was conducted of clinicopathological data from a total of 62 patients with lower uterine segment carcinoma (LUSC) treated at Peking Union Medical College Hospital between March 2016 and November 2023. Among these, 54 formalin-fixed, paraffin-embedded (FFPE) tissue specimens meeting quality criteria were subjected to molecular profiling. DNA was extracted from FFPE samples for next-generation sequencing (NGS), and immunohistochemical (IHC) staining was performed to assess mismatch repair proteins (MLH1, PMS2, MSH2, MSH6), p53, ER, and PR expression. Correlations between molecular subtypes and clinicopathological features—including histological subtype, and clinical outcomes—were evaluated. Additionally, variations in molecular profiles across different editions of the International Federation of Gynecology and Obstetrics (FIGO) staging systems and prognostic risk classifications were analyzed.

Results

(1) A total of 62 patients with LUSC were included in the study, with an average age of 49 years. Symptomatic presentation was observed in 80.6% of cases at initial diagnosis, predominantly manifesting as abnormal uterine bleeding (including irregular vaginal bleeding and postmenopausal bleeding). Histologically, endometrioid carcinoma (75.8%) was the most frequent subtype, with 43.5% classified as aggressive histological variants. Pathological assessment demonstrated that 43.5% of cases exhibited deep myometrial invasion (>50% myometrial thickness), while lymph vascular space invasion (LVSI) and lymph node metastasis were observed in 24.2% and 17.7% of patients, respectively. Immunohistochemical analysis revealed high positivity rates for both estrogen receptor (ER; 77.4%) and progesterone receptor (PR; 69.4%). According to the 2009 FIGO staging criteria, the cases were distributed as follows: stage I (48.4%, 30 cases), stage II (21.0%, 13 cases), stage III (29.0%, 18 cases), and stage IV (1.6%, 1 case).

（2） Molecular classification was successfully performed in 54 LUSC cases through next-generation sequencing and immunohistochemical staining, with the following distribution of molecular classifications: POLE ultra-mutated (POLE mut) in 6 cases (11.1%), Mismatch repair deficiency (MMRd) in 14 cases (25.9%), p53 abnormality (p53 abn) in 9 cases (16.7%), and Non-specific molecular profile (NSMP) in 25 cases (46.3%). Notably, two cases (3.7%) exhibited multiple molecular characteristics, including one case with concurrent POLE mut and p53 abn and another showing combined MMRd and p53 abn.

(3) POLE mut cases (n=6) presented at an average age of 47 years, all with abnormal vaginal bleeding. Histologically, 5 cases (83.3%) were endometrioid endometrial carcinomas (EEC), predominantly poorly differentiated (4/5, 80.0%). Notably, none exhibited LVSI or lymph node metastasis. MMRd tumors (n=14) showed an average age of 45 years, with 78.6% (11/14) EEC, of which 81.8% (9/11) were high-to-intermediate differentiated. The predominant MMR protein loss patterns were: MSH2+MSH6 co-deficiency (50.0%) and MLH1+PMS2 co-deficiency (35.7%). p53 abn subtype (n=9) displayed an average age of 55 years. While 55.6% (5/9) were EEC (80.0% high-to-intermediate differentiated), this group exhibited deep myometrial invasion (≥1/2) in 66.7% (6/9), LVSI in 44.4% (4/9), and lymph node metastasis in 11.1% (1/9). NSMP cases (n=25) had an average age of 49 years, with 80.0% EEC (20/25) and 32.0% aggressive histological variants (8/25). Pathologically, 36.0% (9/25) demonstrated deep myometrial invasion and 8.0% (2/25) had lymph node metastases.

(4) Significant differences were observed among molecular classifications in both histological grading of endometrioid carcinoma (P=0.037) and FIGO staging (2023 version incorporating molecular classification) (P=0.004). POLE mut tumors demonstrated a predominance of high-grade endometrioid endometrial carcinomas (EECs). In contrast, MMRd, p53 abn, and NSMP subtypes showed higher proportions of low-grade EECs.

(5) Changes in the staging of 54 LUSC patients according to the FIGO staging (2009 edition) and FIGO staging (2023 edition) criteria were mainly concentrated in stage I and II cases (12/54, 22.2%), whereas the staging results of patients with stage III and IV remained unchanged. In the new version, 10 patients had their staging upgraded from stage I to stage II, and 2 cases were downgraded from stage II to stage I. Survival analysis showed that the PFS and OS of patients in different FIGO staging criteria were statistically significant (P<0.0001), and stage I had the best prognosis, followed by stage II and III, and stage IV had the worst prognosis.

（6）The prognostic risk grading criteria for 54 patients with LUSC based on unknown molecular classification were 13 (24.1%) low risk, 5 (9.3%) intermediate risk, 14 (25.9%) high-intermediate risk, 21 (38.9%) high risk, and 1 (1.9%) progressive metastasis. According to the prognostic risk grading criteria based on known molecular classification, 17 cases (31.5%) were low risk, 4 cases (7.4%) were intermediate risk, 7 cases (13.0%) were high-intermediate risk, 18 cases (33.3%) were high risk, and 1 case (1.9%) was progressive metastasis. Of these, 5 patients were risk downgraded, and another 5 patients were risk upgraded.

Conclusions

In this study, 54 Chinese LUSC patients were systematically analyzed for molecular classification based on IHC and next-generation sequencing, which is the largest relevant study in China. The results showed that as a rare and unique subtype of endometrial cancer, LUSC had a younger age of onset, higher histological grade, higher incidence of deep myometrial infiltration (≥1/2 myometrium), greater susceptibility to lymph node metastasis, and higher proportion of patients with intermediate and advanced stages. Although the molecular pattern of LUSC was similar to that of UCEC, there were differences in the clinicopathological features corresponding to each molecular subtype. Patients with the NSMP type of LUSC presented a higher clinical risk, the p53 abn type had a complex biological behavior, and the MMRd type had a higher proportion of MSH2 and MSH6 loss, suggesting that it might be of higher relevance to Lynch syndrome, whereas the POLE mut type has similar pathological features to UCEC. The above findings not only deepen the understanding of the biological characteristics of LUSC but also provide a theoretical basis for its stratified management and individualized treatment.