Purpose: RB1 mutations and loss of retinoblastoma (Rb) expression represent consistent but not entirely invariable hallmarks of small cell lung cancer (SCLC). The prevalence and characteristics of SCLC retaining wild-type Rb are not well-established. Furthermore, the performance of targeted next-generation sequencing (NGS) versus immunohistochemistry for Rb assessment is not well-defined. Experimental Design: A total of 208 clinical SCLC samples were analyzed by comprehensive targeted NGS, covering all exons of RB1, and Rb IHC. On the basis of established coordination of Rb/p16/cyclinD1 expression, p16-high/cyclinD1-low profile was used as a marker of constitutive Rb deficiency. Results: Fourteen of 208 (6%) SCLC expressed wild-type Rb, accompanied by a unique p16-low/cyclinD1-high profile supporting Rb proficiency. Rb-proficient SCLC was associated with neuroendocrine-low phenotype, combined SCLC with non-SCLC (NSCLC) histology and aggressive behavior. These tumors exclusively harbored CCND1 amplification (29%), and were markedly enriched in CDKN2A mutations (50%) and NSCLC-type alterations (KEAP1, STK11, FGFR1). The remaining 194 of 208 SCLC were Rb-deficient (p16-high/cyclinD1-low), including 184 cases with Rb loss (of which 29% lacked detectable RB1 alterations by clinical NGS pipeline), and 10 cases with mutated but expressed Rb. Conclusions: This is the largest study to date to concurrently analyze Rb by NGS and IHC in SCLC, identifying a 6% rate of Rb proficiency. Pathologic-genomic data implicate NSCLC-related progenitors as a putative source of Rb-proficient SCLC. Consistent upstream Rb inactivation via CDKN2A/p16↓ and CCND1/cyclinD1↑ suggests the potential utility of CDK4/6 inhibitors in this aggressive SCLC subset. The study also clarifies technical aspects of Rb status determination in clinical practice, highlighting the limitations of exon-only sequencing for RB1 interrogation. See related commentary by Mahadevan and Sholl, p. 4603

中文翻译：

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小细胞肺癌中的 Rb 肿瘤抑制因子：结合基因组和 IHC 分析以及独特的 Rb 丰富子集的描述


目的：RB1 突变和视网膜母细胞瘤 (Rb) 表达缺失代表小细胞肺癌 (SCLC) 的一致但并非完全不变的特征。保留野生型 Rb 的 SCLC 的患病率和特征尚不明确。此外，针对 Rb 评估的靶向下一代测序 (NGS) 与免疫组织化学的性能尚不明确。实验设计：通过综合靶向NGS对总共208个临床SCLC样本进行分析，涵盖RB1和Rb IHC的所有外显子。在已建立的 Rb/p16/cyclinD1 表达协调的基础上，p16-high/cyclinD1-low 被用作组成性 Rb 缺乏的标记。结果：208 例 SCLC 中有 14 例 (6%) 表达野生型 Rb，并伴有支持 Rb 能力的独特 p16-low/cyclinD1-high 特征。 Rb 丰富的 SCLC 与神经内分泌低表型、SCLC 与非 SCLC (NSCLC) 组织学和攻击行为相结合。这些肿瘤仅存在 CCND1 扩增 (29%)，并且显着富含 CDKN2A 突变 (50%) 和 NSCLC 型改变（KEAP1、STK11、FGFR1）。 208例SCLC中的其余194例为Rb缺陷（p16高/cyclinD1低），其中184例Rb缺失（其中29%缺乏临床NGS管道可检测到的RB1改变），以及10例突变但表达Rb。结论：这是迄今为止在 SCLC 中通过 NGS 和 IHC 同时分析 Rb 的最大研究，确定 Rb 熟练率为 6%。病理基因组数据表明 NSCLC 相关祖细胞是 Rb 丰富的 SCLC 的推定来源。通过 CDKN2A/p16↓ 和 CCND1/cyclinD1↑ 一致的上游 Rb 失活表明 CDK4/6 抑制剂在这种侵袭性 SCLC 亚群中的潜在用途。 该研究还阐明了临床实践中 Rb 状态测定的技术问题，强调了仅外显子测序用于 RB1 询问的局限性。参见 Mahadevan 和 Sholl 的相关评论，第 17 页。 4603