Lymphatic vessel distribution in the mucosa and submucosa and potential implications for T1 colorectal tumors.

ABSTRACT

PURPOSE: Colorectal cancer spreads to lymph nodes via surrounding lymphatic vasculature. Once this spread has occurred, the prognosis of the patient is significantly worse. Lymphatics are difficult to identify on hematoxylin and eosin stains and lack of specific markers has meant that little is known about their distribution in colorectal tissue. The national bowel cancer screening program has resulted in an increase in the diagnosis of T1 colorectal cancers. Patients with suitable T1 tumors can avoid bowel resections and their associated morbidity with the advances in local resection techniques. This means, however, that formal staging and lymph node assessment cannot be performed. Prognostic tools are required to predict risk of lymph node metastases. Studies assessing risk of lymph node spread in T1 tumors have found that invasion of the tumor into the deepest third of the submusosa affords a much greater risk. We hypothesized that this might be due to the quantity or characteristics of lymphatic vasculature in this third. METHODS: A specific lymphatic marker, D2-40 was applied to 5-µm sections of normal colorectal tissue from 45 patients. Slides were scanned and analyzed using Aperio's ImageScope software for PC. Analysis boxes of fixed area were placed within the mucosal layer and within each third of the submucosal layer allowing characteristics of the lymphatics in each third to be quantified individually. RESULTS: Lymphatic vessels were found in the mucosal layer of all samples although these were significantly smaller than the submucosal vessels (P = .0005). Lymphatics were significantly more numerous in the superficial third of the submucosa (P = .0005); however, vessel size was similar in Sm1, Sm2, and Sm3. CONCLUSION: The deepest third of the submucosa contains the smallest number of lymphatic vessels despite invasion into this layer being associated with a higher risk of lymph node spread.