Enhancement of Tumorigenicity with Morphological Progression in a BALB/c Preneoplastic Outgrowth Line

Four newly established mammary hyperplastic outgrowth lines were analyzed for their tumorigenic, morphological, and ovarian hormone-dependent growth properties in BALB/cMed mice. The mammary outgrowth lines were designated DIM-1, DIM-2, DIM-3, and DIM-4 to indicate their origin from the mammary cell line COMMA-D. DIM-1, DIM-2, and DIM-3 were classical hyperplastic alveolar outgrowth lines that possessed high tumor-producing capabilities and rapidly evolved by transplant generation (TG) 6 into ovarian hormone-independent populations. DIM-3 was also characterized by extensive formation of dilated (cystic) alveoli. This characteristic did not correlate either positively or negatively with the tumor-producing capabilities of these lines. DIM-4 was a ductal outgrowth line that exhibited a progression in several biological properties. This line progressed morphologically from a ductal outgrowth to a mixed outgrowth of small ducts (ductules) with scattered alveoli and then in subsequent passages to a uniform alveolar outgrowth. Concurrent with these morphological changes, the tumor-producing capabilities of DIM-4 increased from low [40% with the time for 50% of the transplants to produce mammary tumors (TE50) greater than 12 mo] to high (71% with a TE50 of 7.1 mo). The ductal outgrowth line (TG 4) was totally dependent on ovarian hormones for growth; however, later passages (TG 8) of DIM-4 were only partially ovarian hormone dependent for growth and ovarian hormone independent for maintenance of alveolar morphology. In addition, the tumorigenic response to 7,12-dimethylbenz[a]anthracene (CAS: 57-97-6) was low in the ductal stage (TG 4) and high in the alveolar stage (TG 7). The results demonstrate an enhancement of tumorigenicity with morphological and biological progression in a preneoplastic mammary cell population and support the hypothesis that the cells at high risk for tumorigenesis in the BALB/c mammary gland appear to be the alveolar cell type.