Background

Integrated PET/MRI is a promising modality for breast assessment. The most frequently used tracer, fluorine 18 (¹⁸F) fluorodeoxyglucose (FDG), is applied for whole-body staging in advanced breast cancer but has limited accuracy in evaluating primary breast lesions. The fibroblast-activation protein (FAP) is abundantly expressed in invasive breast cancer. FAP-directed PET tracers have recently become available, but results in primary breast tumors remain lacking.

Purpose

To evaluate the use of FAP inhibitor (FAPI) breast PET/MRI in assessing breast lesions and of FAPI whole-body scanning for lymph node (LN) and distant staging using the ligand gallium 68 (⁶⁸Ga)-FAPI-46.

Materials and Methods

In women with histologically confirmed invasive breast cancer, all primary ⁶⁸Ga-FAPI-46 breast and whole-body PET/MRI and PET/CT examinations conducted at the authors’ center between October 2019 and December 2020 were retrospectively analyzed. MRI lesion characteristics and standardized uptake values (SUVs) were quantified with dedicated software. Mann-Whitney U tests were used to compare tumor SUVs across different tumor types. The Pearson correlation coefficient was calculated between SUV and measures of MRI morphologic characteristics.

Results

Nineteen women (mean age, 49 years ± 9 [standard deviation]) were evaluated—18 to complement initial staging and one for restaging after therapy for distant metastases. Strong tracer accumulation was observed in all 18 untreated primary breast malignancies (mean maximum SUV [SUV_max] = 13.9 [range, 7.9–29.9]; median lesion diameter = 26 mm [range, 9–155 mm]), resulting in clear tumor delineation across different gradings, receptors, and histologic types. All preoperatively verified LN metastases in 13 women showed strong tracer accumulation (mean SUV_max= 12.2 [range, 3.3–22.4]; mean diameter = 21 mm [range, 14–35 mm]). Tracer uptake established or supported extra-axillary LN involvement in seven women and affected therapy decisions in three women.

Conclusion

This retrospective analysis indicates use of ⁶⁸Ga fibroblast-activation protein inhibitor tracers for breast cancer diagnosis and staging.

© RSNA, 2021

Online supplemental material is available for this article.

See also the editorial by Mankoff and Sellmyer in this issue.

中文翻译：

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针对乳腺癌成纤维细胞激活蛋白的同步 FAPI PET/MRI

背景

综合 PET/MRI 是一种很有前途的乳房评估方式。最常用的示踪剂氟 18 ( ¹⁸ F) 氟脱氧葡萄糖 (FDG) 应用于晚期乳腺癌的全身分期，但在评估原发性乳腺病变方面的准确性有限。成纤维细胞激活蛋白 (FAP) 在浸润性乳腺癌中大量表达。FAP 定向的 PET 示踪剂最近已经可用，但仍然缺乏对原发性乳腺肿瘤的结果。

目的

评估 FAP 抑制剂 (FAPI) 乳腺 PET/MRI 在评估乳腺病变和 FAPI 全身扫描淋巴结 (LN) 和使用配体镓 68 ( ⁶⁸ Ga)-FAPI-46 的远处分期中的应用。

材料和方法

在组织学证实为浸润性乳腺癌的女性中，回顾性分析了 2019 年 10 月至 2020 年 12 月在作者中心进行的所有原发性⁶⁸ Ga-FAPI-46 乳房和全身 PET/MRI 和 PET/CT 检查。使用专用软件对 MRI 病变特征和标准化摄取值 (SUV) 进行量化。Mann-Whitney U检验用于比较不同肿瘤类型的肿瘤 SUV。计算 SUV 和 MRI 形态特征测量值之间的 Pearson 相关系数。

结果

对 19 名女性（平均年龄，49 岁 ± 9 [标准差]）进行了评估，其中 18 名用于补充初始分期，1 名用于治疗远处转移后的再分期。在所有 18 例未治疗的原发性乳腺恶性肿瘤中观察到强示踪剂积累（平均最大 SUV [SUV _max ] = 13.9 [范围，7.9-29.9]；中位病变直径 = 26 mm [范围，9-155 mm]），导致肿瘤清晰不同分级、受体和组织学类型的描述。13 名女性术前证实的所有 LN 转移灶均显示出强烈的示踪剂积聚（平均 SUV_最大值= 12.2 [范围，3.3-22.4]；平均直径 = 21 mm [范围，14-35 mm]）。示踪剂摄取确定或支持了 7 名女性的腋外淋巴结受累，并影响了 3 名女性的治疗决策。

结论

该回顾性分析表明使用⁶⁸ Ga 成纤维细胞活化蛋白抑制剂示踪剂进行乳腺癌诊断和分期。

© 北美放射学会，2021

本文提供在线补充材料。

另见本期 Mankoff 和 Sellmyer 的社论。