Biological significance of isolated tumor cells and micrometastasis in lymph nodes evaluated using a green fluorescent protein-tagged human gastric cancer cell line.
OBJECTIVE
The biological significance of isolated tumor cells and micrometastasis in lymph node defined by the International Union against Cancer remains essentially unknown because of the lack of appropriate animal models. In the present study, we developed a lymph node micrometastasis model featuring a human gastric cancer cell line tagged with green fluorescent protein gene (GCIY-EGFP), which allows visualization of even isolated tumor cells in the development of metastasis without histologic procedure. Using this model, we investigated the effect of surgery and chemotherapy on the growth of early-phase metastasis formation in the lymph nodes.


METHODS
The time course of spontaneous inguinal lymph node metastasis after s.c. inoculation of GCIY-EGFP cells into nude mice was examined with fluorescence dissecting microscopy. Then, the effects of surgical removal of the primary tumor with or without anti-asialo GM1 treatment or postoperative chemotherapy on the growth of isolated tumor cells and micrometastasis in the lymph nodes were examined.


RESULTS
GCIY-EGFP cells were found to metastasize spontaneously to the inguinal lymph nodes to form isolated tumor cells, micrometastasis, and, finally, develop macroscopic metastasis at 1 to 2, 3 to 5, and 5 weeks postinjection, respectively. When the primary tumors were removed within 2 weeks of inoculation, isolated tumor cells, but not micrometastasis, in the lymph nodes regressed by 4 weeks after surgery in all the mice examined (five of five). This spontaneous regression of isolated tumor cells was completely reversed by anti-asialo GM1 treatment, which could deplete natural killer cells effectively in nude mice. Chemotherapy following resection of the primary tumor at an early stage partially eliminated the remaining micrometastasis in the lymph nodes.


CONCLUSIONS
These results suggest that isolated tumor cells in the regional lymph nodes regressed by removal of the primary tumor mainly via natural killer cell-mediated antitumor activity and that micrometastasis in the lymph nodes could be effectively eliminated by the postoperative chemotherapy.
Yokoyama
Hiroyuki
H
Department of Surgery II, Nagoya University School of Medicine and Division of Oncological Pathology, Aichi Cancer Center Research Institute, Kanokoden, Chukisa-ku, 464-8681 Nagoya, Japan.
Nakanishi
Hayao
H
Kodera
Yasuhiro
Y
Ikehara
Yuzuru
Y
Ohashi
Norifumi
N
Ito
Yuichi
Y
Koike
Masahiko
M
Fujiwara
Michitaka
M
Tatematsu
Masae
M
Nakao
Akimasa
A
D000818:Animals; D000911:Antibodies, Monoclonal / Q000627:therapeutic use; D005677:G(M1) Ganglioside / Q000276:immunology; D005743:Gastrectomy; D049452:Green Fluorescent Proteins; D006801:Humans; D007694:Killer Cells, Natural / Q000276:immunology; D008197:Lymph Node Excision; D008198:Lymph Nodes; D008207:Lymphatic Metastasis; D008297:Male; D051379:Mice; D008819:Mice, Nude; D009367:Neoplasm Staging; D009368:Neoplasm Transplantation; D011182:Postoperative Care; D012878:Skin Neoplasms / Q000473:pathology*; D013274:Stomach Neoplasms / Q000473:pathology*; D014407:Tumor Cells, Cultured
D000911:Antibodies, Monoclonal; C485184:enhanced green fluorescent protein; D049452:Green Fluorescent Proteins; D005677:G(M1) Ganglioside; C018835:asialo GM1 ganglioside