Metastatic Growth of a Murine Tumor: Evidence of Dissemination to the Lungs in the Absence of Subcutaneous Growth

Abstract

Growth of MCA-38/B colon adenocarcinoma was detectable 30-33 days after subcutaneous (s.c.) tumor cell inoculation in mice. Seventy percent of the mice receiving 10⁷ tumor cells, 50 % of those receiving 10⁴, and 15% of the mice given 10⁵ cells developed s.c. tumors (mean of 4 experiments, total of 80 mice per group). Metastases in the presence of a primary tumor were observed in 11% of 10⁷ and in 10% of 10⁶ tumor-cell injected animals. Lung metastases were detected in the absence of tumor growth at the site of s.c. cell injection in 19% of 10⁷, in 8% of 10⁶ and in 5% of 10⁵ and 10⁴ tumor-cell inoculated mice. In parallel experiments an intravenous (i.v.) inoculum of tumor cells produced lung colonies in 40% of 10⁶ and in 14% of 10⁵ tumor-cell injected animals. Smaller inocula did not give rise to lung colonies, thus making it unlikely that accidental i.v. inoculations of tumor cells during the s.c. injections caused the observed metastatic dissemination to the lungs.