Reply to the Letter of Dr. Cho et al.

We are happy to thank the Korean team from Seoul for their very pertinent comment. They draw attention to the limited reliability of the assessment of the depth of invasion of a cancer in a specimen resected during endoscopy. The established cutoff limits for safety of endoscopic treatment (200 µm in esophagus, 500 µm in stomach and 1000 µm in colon) are based on surgical series, and are preferred to the semiquantitative estimation in three sectors of the submucosa (superficial, middle, and deep, or sm1, sm2, and sm3 sectors). In fact, when surgical specimens, with full thickness of the submucosa and full thickness of the digestive wall, are stretched in a support, prior to fixation in formalin, their elasticity is limited. Pathology studies have confirmed that the risk of lymphatic metastases is very low, when invasion is less than the cutoff limit.

In contrast, mucosectomy specimens involve only the superficial layers of the digestive wall, and the resection of the submucosa is incomplete as a rule (the exception being when the submucosal dissection technique is used). Qualitative estimation in the sm1, sm2, and sm3 layers is not a reliable means of assessing the risk of lymphatic metastases. On the other hand, the elasticity of these specimens is maximal and variations in the diameter and thickness of the layers occur during stretching; this may impair the reliability of measurement of depth of invasion by the micrometric method. The method proves reliable if the specimen is gently placed (flat out) on the support and not stretched. In the stomach, the 500 µm cutoff value is a maximal figure for the safety of the procedure. The cutoff value should be reduced in proportion to the degree of stretching. Of course this also applies to mucosectomy specimens obtained in the esophagus or the colon. In conclusion, one must not attempt to flatten the mucosectomy specimen on its support by applying a strong stretching.