Differential Influence of Organ Site on Three Subpopulations of a Single Mouse Mammary Tumor at Two Distinct Steps in Metastasis

Tumor subpopulations 66c14, 168FARN, and 4T07 are drug-resistant variants selected from sister subpopulations derived from a single mouse mammary tumor. These subpopulations are heterogeneous in their capacities to form experimental metastatic growth in the lungs and liver. Initial survival kinetics of arrested cells, determined by the clearance of 125IUdR-labelled cells, and subsequent growth rates, determined by sequential recovery of clonogenic tumor cells from occult metastases, both correlated with organ-colonizing potential as determined by necropsy. The growth rates of these 3 subpopulations were determined in vitro in monolayer and in situ in the subcutis, in the liver following intrasplenic injection, and in the lung following intravenous injection. Clonogenic potential of all 3 lines was similar in vitro (54-59%). Growth rates in vitro (population doubling times 16.5-21 hr) and in the subcutis (tumor volume doubling times 5.2-7.4 days) were similar for the 3 subpopulations, but differed significantly in the liver and lungs. For line 4T07, the most metastatic line to both lung and liver, population doubling times in vitro and in the lung and liver were similar, ranging from 17 to 26 hr. For lines 66c14 and 168FARN, the growth rates in lungs and livers were much slower than in vitro. Line 66c14, which is relatively more metastatic to the lungs, grew much faster in the lung (39 hours) than in the liver (91 hr), but line 168FARN, which is relatively more metastatic to the liver, grew at a faster rate in the liver (37 hr) than in the lung (63 hr). Thus, 3 tumor subpopulations (seeds) derived from a single tumor were differentially affected by host organ factors (soil) at 2 distinct stages in the metastatic process.