The TNM classification defines micrometastasis (MM) and isolated tumor cells (ITC) in lymph nodes (LN). Sentinel node (SN) navigation surgery has been introduced in gastrointestinal cancer. Few reports have examined the morphological distribution of MM and ITC of SN in gastric cancer. The purpose of this study was to clarify the clinical significance of the morphological distribution of cancer cells in SNs according to metastasis (MA), MM, and ITC.
All dissected LNs obtained from 160 consecutive patients with mapped SNs arising from cT1-2 N0 tumors were examined. Metastasis in these LNs was examined by histology and cytokeratin staining. The distribution of MA, MM, and ITC was classified as marginal sinus (MS), intermediate sinus (IS), parenchymal (PA), and diffuse types (DF).
Nodal metastases were detected in 65 SNs from 30 patients and MA, MM, and ITC accounted for 53.9%, 21.5%, and 24.6%, respectively. MS, IS, PA, and DF accounted for 57%, 6%, 17%, and 20.0%, respectively. Patients with metastasis of non-MS had more nodal metastasis in non-SNs (P = .025) and had nodal metastasis in second tier (P = .009), compared with the patients with metastasis of MS. The incidence of metastasis in non-MS was higher in tumors larger than 40 mm than those smaller than 40 mm (P = .011).
When performing SN navigation surgery in gastric cancer, we should keep in mind that the patients with tumor larger than 40 mm in size and nodal metastasis of non-MS may have non-SN metastasis and nodal metastasis in second tier.