虽然延误诊断并不一定意味着预后更差，但如果怀疑有胃癌就应该立即进行诊断性评估。

内镜检查 — 上消化道内镜是解剖学定位原发灶及组织学诊断的最佳方法(图1，图2)。虽然上消化道内镜费用更高且侵入性更强，但其对于多种胃、食管以及十二指肠病变诊断的敏感性和特异性也要比其他诊断方法(如钡剂造影检查，见下文)更强。对有消化道症状的患者尽早进行上消化道内镜检查可能提高早期胃癌的检出率。

图1：Malignant and benign gastric ulcer: Endoscopic appearance

Endoscopy showing the differences between the endoscopic appearance of malignant and benign gastric ulcers.
(A) Retroflexed views were required on endoscopy to detect this malignant gastric ulcer of the cardia. Note the absence of folds radiating to the base and the exophytic appearance. Biopsies confirmed the presence of adenocarcinoma.
(B) Benign gastric ulcer in the prepyloric region. The ulcer is well circumscribed, with folds radiating to the ulcer base.

图2：Endoscopic appearances of gastric cancer

Endoscopy shows different appearances of a gastric adenocarcinoma.
(Upper panel) Adenocarcinoma in the antrum manifested by a friable, ulcerated, and circumferential mass.
(Lower panel) Adenocarcinoma of the cardia. This large, lobulated, ulcerated mass was seen only by retroflexed views of the gastroesophageal junction.

内镜可以在检查的同时取活检，这增加了其临床实用性。鉴于高达5%的恶性溃疡大体表现为良性，因此所有这类病变均有必要进行活检和组织学评估。

内镜技术 — 内镜检查过程中发现任何外观可疑的胃溃疡均应留取活检。单次活检对于诊断现有胃癌的敏感性约为70%，而在溃疡边缘及基底部取7块活检可将诊断的敏感性提高到98%以上。不但应对所有外观可疑的病变取活检，更应对外观呈良性的小溃疡取多个活检，因为诊断出早期胃癌才能尽可能提高手术治愈率及长期存活率。

内镜下诊断高度侵袭性的弥漫型胃癌(即“皮革胃”)有一定难度。因为此类肿瘤往往会浸润黏膜下层及固有肌层，表浅黏膜活检可能出现假阴性。因此，如果怀疑弥漫型胃癌，应采用剥取活检联合咬取活检进行检查[15]。胃扩张性差或是食管吞钡造影中有特征性改变(皮革烧瓶样改变)可能提示该病。

刷片细胞学检查可提高单次活检的敏感性，但在取7块活检时，其对诊断检出率的帮助有多大仍不明确。如果内镜医师担心活检会造成出血，可以对溃疡基底部进行刷检，因为这种操作的出血风险非常小。

胃溃疡内镜随访需求 — 确诊胃溃疡患者的内镜随访检查指征详见其他专题。

钡剂造影检查 — 钡剂造影检查可以发现恶性胃溃疡及浸润性病变，有时亦可发现早期胃癌(图2)。然而，高达50%的病例钡剂检查可出现假阴性。对于早期胃癌患者来说更是如此，钡剂检查对这类病变的敏感性可能只有14%[18]。因此在大多数情况下对于疑似胃癌的患者，上消化道内镜才是首选的初始诊断性检查。

图2：Early gastric cancer as seen on upper gastrointestinal (UGI) series

A double contrast upper gastrointestinal study shows a superficial ulcer in the gastric antrum (arrow) with thickened folds radiating towards the ulcer.

但患者出现“皮革胃”时，钡剂造影检查优于上消化道内镜。僵硬的“皮革烧瓶样”胃的扩张性下降，这在影像学检查中更为明显，而其内镜表现可能相对正常(图3、图4)。

图3：Linitis plastica of the stomach as seen on UGI series

UGI study reveals fixed narrowing of the entire proximal stomach (arrows) due to submucosal invasion by a gastric cancer. Other malignancies, such as breast and lung metastases to the stomach, may have a similar appearance.

图4：Normal upper GI series

Normal air-contrast upper GI study showing normal gastric folds and small intestinal anatomy, and no masses.
GI: gastrointestinal.