Accurate staging of invasive lobular carcinoma (ILC), a subtype of breast cancer, is vital for effective clinical management. Although ¹⁸F-FDG PET/CT is a commonly used tool, its efficacy varies across different histologic subtypes. To mitigate this challenge, our investigation delves into the potential utility of ⁶⁸Ga-fibroblast activation protein inhibitor (FAPI) PET/CT as an alternative for staging ILC, aiming to address a significant research gap using a more expansive patient cohort than the smaller samples commonly found in the existing literature. Methods: In this retrospective analysis, women diagnosed with primary ILC of the breast underwent both ¹⁸F-FDG PET/CT and ⁶⁸Ga-FAPI PET/CT. Both modalities were compared across all lesion locations with the used reference standard. The interval between scans was 1 wk, without any intervening treatments. Lesions were categorized visually, and tracer activity was analyzed using SUV_max, tumor-to-background uptake ratio, and uptake ratios. Both modalities were compared across various parameters, and statistical analysis was performed using SPSS 22.0. A P value of less than 0.05 was chosen to determine statistical significance. Results: The study included 23 female ILC patients (mean age, 51 y) with hormone-positive, human epidermal growth factor receptor type 2–negative tumors. Most (65%) had the luminal A subtype. ⁶⁸Ga-FAPI PET/CT outperformed ¹⁸F-FDG PET/CT, with higher tumoral activity and tumor-to-background uptake ratios (P < 0.001). Primary tumors showed significantly increased uptake with ⁶⁸Ga-FAPI PET/CT (P < 0.001), detecting additional foci, including multicentric cancer. Axillary lymph node metastases were more frequent and had higher uptake values with ⁶⁸Ga-FAPI PET/CT (P = 0.012). Moreover, ⁶⁸Ga-FAPI PET/CT identified more lesions, including bone and liver metastases. Pathologic features did not significantly correlate with imaging modalities, but a positive correlation was observed between peritumoral lymphocyte ratio and ⁶⁸Ga-FAPI PET/CT–to–¹⁸F-FDG PET/CT uptake ratios (P = 0.026). Conclusion: This study underscores ⁶⁸Ga-FAPI PET/CT’s superiority over ¹⁸F-FDG PET/CT for ILC. ⁶⁸Ga-FAPI PET/CT excels in detecting primary breast masses, axillary lymph nodes, and distant metastases; can complement ¹⁸F-FDG PET/CT in ILC; and holds potential as an alternative imaging method in future studies.

浸润性小叶癌（ILC）（乳腺癌的一种亚型）的准确分期对于有效的临床管理至关重要。尽管¹⁸ F-FDG PET/CT 是常用的工具，但其功效因不同组织学亚型而异。为了缓解这一挑战，我们的研究深入探讨了⁶⁸ Ga 成纤维细胞激活蛋白抑制剂 (FAPI) PET/CT 作为 ILC 分期替代方案的潜在效用，旨在使用比较小样本更广泛的患者队列来弥补重大研究空白现有文献中常见。方法：在这项回顾性分析中，诊断为乳腺原发性 ILC 的女性接受了¹⁸ F-FDG PET/CT 和⁶⁸ Ga-FAPI PET/CT。将所有病变位置的两种方式与所使用的参考标准进行比较。扫描间隔为1周，不进行任何干预治疗。对病变进行视觉分类，并使用 SUV _max、肿瘤与背景摄取比和摄取比来分析示踪剂活性。对两种模式的各种参数进行比较，并使用 SPSS 22.0 进行统计分析。选择小于 0.05 的P值来确定统计显着性。结果：该研究纳入了 23 名患有激素阳性、人表皮生长因子受体 2 型阴性肿瘤的女性 ILC 患者（平均年龄 51 岁）。大多数 (65%) 具有管腔 A 亚型。⁶⁸ Ga-FAPI PET/CT 优于¹⁸ F-FDG PET/CT，具有更高的肿瘤活性和肿瘤背景摄取比（P < 0.001）。原发性肿瘤显示⁶⁸ Ga-FAPI PET/CT 的摄取显着增加（P < 0.001），检测到其他病灶，包括多中心癌症。腋窝淋巴结转移更频繁，⁶⁸ Ga-FAPI PET/CT 摄取值更高（P = 0.012）。此外，⁶⁸ Ga-FAPI PET/CT 发现了更多病变，包括骨转移和肝转移。病理特征与成像方式没有显着相关性，但瘤周淋巴细胞比率与⁶⁸ Ga-FAPI PET/CT 与¹⁸ F-FDG PET/CT 摄取比率呈正相关（ P = 0.026）。结论：本研究强调⁶⁸ Ga-FAPI PET/CT 在 ILC 方面优于¹⁸ F-FDG PET/CT。⁶⁸ Ga-FAPI PET/CT 擅长检测原发性乳腺肿块、腋窝淋巴结和远处转移；可以补¹⁸ILC 中的 F-FDG PET/CT；并在未来的研究中具有作为替代成像方法的潜力。