Growth patterns and metastatic behavior of human tumors growing in athymic mice

The growth characteristics and metastatic behavior of human tumors growing in athymic nude mice were studied. Human tumor cell lines HEp-2 (carcinoma or larynx) and SW480 (colon carcinoma) were transplanted into athymic nude mice of BALB/c origin. Tumor cells (1 x 10(6) and 2 x 10(7)) were given either s.c. or i.p. Following s.c. injection tumors developed rapidly to become easily palpable with 2 weeks forming a s.c. tumor focus surrounded by a thick fibrous capsule. Animals with s.c. transplants were little affected by the growing tumor. At the time they were sacrificed at Day 34 (HEp-2) and 62 (SW480), a large part of the tumor was necrotic. Capsular infiltration and invasion of lymphatic vessels and perineural and perivascular lymphatic spaces were observed. Metastases to regional lymph nodes were seen in animals kept alive for up to 6 months. Following i.p. transplantation, tumors spread widely in the peritoneal cavity, invaded intraabdominal organs, and metastasized to mediastinal lymph nodes and lungs. Fifteen of 26 animals (60%) developed metastases. Necrosis of the i.p. growing tumors was minimal. All animals in this group died as a result of tumor growth.