Background/Objectives: Pembrolizumab demonstrates a high response rate in patients with mismatch repair-deficient (dMMR) metastatic colorectal cancer (mCRC), with responses often sustained even after treatment cessation. However, the pathological complete response (pCR) rate in clinically responding cases remains unknown. This study aimed to evaluate the relationship between the radiological and pathological responses in patients with dMMR mCRC who responded to pembrolizumab.Methods: This retrospective study included 27 patients with dMMR mCRC treated with pembrolizumab. The radiological response was assessed using RECIST version 1.1 criteria. The pathological response was evaluated in patients who underwent metastasectomy, with pCR defined as the absence of residual cancer cells.Results: The median progression-free survival (PFS) of the cohort was 19 months. Among the 27 patients, 3 achieved clinical complete response (cCR), and 10 had clinical partial response (cPR), resulting in a response rate of 48%. All three patients with cCR maintained their responses without metastasectomy (2-year PFS: 100%). Among patients with cPR, eight maintained their responses, while two experienced progression (2-year PFS: 75%). Five patients with cPR underwent curative-intent metastasectomy, and four of them (80%) achieved pCR. Thus, at least 40% of patients with cPR in this cohort had no residual cancer histologically.Conclusions: Our findings demonstrate the significant discordance between the radiological and pathological responses to pembrolizumab in dMMR mCRC patients, with 80% of those with cPR achieving pCR upon metastasectomy. These observations highlight the need for improved response assessment methods for precision immunotherapy.
背景/目的：帕博利珠单抗在错配修复缺陷型(dMMR)转移性结直肠癌(mCRC)患者中显示出较高的应答率，且应答常在治疗停止后仍持续存在。然而，临床应答病例的病理完全缓解(pCR)率仍不明确。本研究旨在评估对帕博利珠单抗产生应答的dMMR mCRC患者的影像学应答与病理学应答之间的关系。 方法：这项回顾性研究纳入了27例接受帕博利珠单抗治疗的dMMR mCRC患者。影像学应答采用RECIST 1.1版标准进行评估。对接受转移灶切除术的患者进行病理学应答评估，pCR定义为无残留癌细胞。 结果：该队列的中位无进展生存期(PFS)为19个月。在27例患者中，3例达到临床完全缓解(cCR)，10例达到临床部分缓解(cPR)，总应答率为48%。所有3例cCR患者均未行转移灶切除术而维持应答(2年PFS：100%)。在cPR患者中，8例维持应答，2例出现进展(2年PFS：75%)。5例cPR患者接受了以治愈为目的的转移灶切除术，其中4例(80%)达到pCR。因此，该队列中至少40%的cPR患者在组织学上无残留癌。 结论：我们的研究结果表明，在dMMR mCRC患者中，对帕博利珠单抗的影像学应答与病理学应答存在显著不一致性，80%的cPR患者在转移灶切除术后达到pCR。这些观察结果凸显了改进精准免疫治疗应答评估方法的必要性。
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