Gastric foveolar-type adenoma (FA) is a rare benign neoplasm occurring either sporadically or in patients with familial adenomatous polyposis (FAP). However, the molecular features of FA and the relationship between sporadic and syndromic lesions remain unclear. In this study, we performed clinicopathological, immunohistochemical, and genetic analyses of 18 sporadic and 30 FAP-associated FAs. Most sporadic and FAP-associated FAs were located in the upper or middle third of the stomach, on a background of fundic gland mucosa. Most lesions were low-grade, but 3 lesions had a high-grade component. Sporadic FAs included 2 morphologically distinct subtypes, that is, flat and raspberry-like FAs, which we distinguished based on the endoscopic features. Seven lesions were regarded as flat FAs, appearing as large, slightly elevated lesions and measuring 11 to 87 mm in size. Conversely, 10 raspberry-like FAs were small bright-red polyps, measuring 2 to 8 mm in size. FAP-associated FAs, particularly larger lesions, exhibited morphologic features resembling flat FAs but varied significantly in size (2 to 103 mm). Mutation analysis identified APC and KRAS mutations in all flat FAs but never in raspberry-like FAs. Remarkably, somatic APC and KRAS mutations were also detected in 19 (63%) and 27 (90%) of FAP-associated FAs, respectively. This indicates that they are genetically equivalent to sporadic, flat FAs. This study showed that sporadic FA includes at least 2 morphologically and genetically distinct subtypes: flat and raspberry-like FA. Furthermore, flat FA represents a sporadic counterpart of FAP-associated FA.

胃小凹型腺瘤 (FA) 是一种罕见的良性肿瘤，偶发或发生在家族性腺瘤性息肉病 (FAP) 患者身上。然而，FA 的分子特征以及散发性和综合征性病变之间的关系仍不清楚。在这项研究中，我们对 18 例散发性和 30 例 FAP 相关 FA 进行了临床病理学、免疫组织化学和遗传学分析。大多数散发性和 FAP 相关的 FA 位于胃的上三分之一或中三分之一，在胃底腺粘膜的背景上。大多数病变为低级别，但 3 个病变具有高级别成分。散发性 FA 包括 2 种形态学上不同的亚型，即扁平和覆盆子样 FA，我们根据内窥镜特征对其进行了区分。七个病灶被视为平坦的 FA，看起来很大，轻微隆起的病变，尺寸为 11 至 87 毫米。相反，10 个类似覆盆子的 FA 是鲜红色的小息肉，大小为 2 至 8 毫米。FAP 相关的 FA，尤其是较大的病变，表现出类似于扁平 FA 的形态学特征，但大小差异很大（2 至 103 毫米）。确定突变分析所有扁平 FA 中的APC和KRAS突变，但从未在类覆盆子 FA 中发生。值得注意的是，还在 19 个 (63%) 和 27 个 (90%) 的 FAP 相关 FA 中分别检测到体细胞APC和KRAS突变。这表明它们在遗传上等同于零星的扁平 FA。这项研究表明，散发性 FA 至少包括 2 种形态学和遗传学上不同的亚型：扁平型和覆盆子样 FA。此外，扁平 FA 代表 FAP 相关 FA 的零星对应物。