Two human colonic adenocarcinoma cell lines were propagated in the Rowett athymic rat. Line LoVo displayed a well-differentiated morphology and exhibited progressive growth over a 70-day observation period with a doubling time of 8.5 days throughout. No metastatic involvement was noted.

Xenografts of SW 620 cells were undifferentiated and highly necrotic. These tumors grew progressively for approximately 30 days with a doubling time of 5.5 days, but over 90% of the animals exhibited a spontaneous regression with a mean time to total regression of 51 ± 3 (S.E.) days. Animals which had rejected the SW 620 xenografts would not support the growth of either the SW 620 or LoVo xenografts when challenged a second time with inocula producing a 100% tumor incidence in control rats. No metastatic involvement was noted for the SW 620 xenografts, but the tumors frequently invaded the underlying musculature and protruded into the peritoneal cavity without producing ascites or tumor nodules at sites distant from the primary.

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Supported in part by BRSG Grant RR5511-18, CA 11520, and CA 14528 from the National Cancer Institute.

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