CLIN. EXPL. METASTASIS, 1983, VOL. 1, NO. 4, 373 380 TS/A: a BALB/c new metastasizing cell line from a spontaneous mammary adenocarcinoma PATRIZIA NANNI, CARLA DE GIOVANNI, PIER-LUIGI LOLLINI, GIORDANO NICOLETTI and GIORGIO PRODI Istituto di Cancerologia, Universitfi di Bologna, V.le Filopanti 22, 1-40126 Bologna, Italy (Received 17 May 1983; accepted 18 August 1983) A metastasizing mouse cell line (TS/A), originated from a mammary adeno- carcinoma which arose spontaneously in a BALB/c female retired breeder, has been established in vitro. It displayed a remarkable morphologic hetero- geneity, which is evident in plastic adherent cultures (cell types ranging from epithelial-like to fibroblast-like) as well as in semi-solid agar cultures. The TS/A line exhibited the presence of specific cytoplasmic estradiol receptor, with a binding activity of 16 fmoles/mg cytosol protein. The in vivo growth pattern was as follows: (1) a s.c. inoculum of 105 cells caused a 100 per cent tumor take and kill in syngeneic animals; mean survival time was 54+1 days; (2) it did not show significant transplant immunogenicity in syngeneic animals; (3) it was able to give rise to both spontaneous lung metastases and artificial lung colonies; (4) it had a high capacity to grow in H-2 matched, minor histocompatibility antigen incompatible hosts (106 cells killed 100 per cent DBA/2 mice in 58 + 2 days). This line of spontaneous mammary tumor cells is proposed as a useful model for studies on the heterogeneity of the neoplastic population in relation to metastatic spread, on tumor immunogenicity, and on therapy of mammary neoplasia. Introduction Most experimental studies on cancer biology, immunology and genetics are carried out with animal tumors artificially induced by chemical carcinogens, viruses or radiation. The same studies performed with spontaneous tumors sometimes give contrasting results: for example, induced tumors frequently show a high transplantation immunogenicity, whereas spontaneous tumors do not elicit a demonstrable resistance [3, 11]. Therefore, well characterized spontaneous animal tumors are more 'realistic' models for the study of human tumors [12]. We established in vitro a new metastasizing cell line derived from a mouse mammary adenocarcinoma which had arisen spontaneously in a BALB/c female retired breeder. Because of the whole pattern of its characteristics, this line is proposed here as a new model for studies on the immunology and on the metastatic behaviour of mammary tumor; moreover, it could constitute a valid test system for the various protocols of experimental therapy. Materials and methods Mice Except when otherwise specified, 8-16 weeks-old female mice of the following strains were used: BALB/cAnNCrlBR, DBA/2NCrlBR,C57BL/6NCrlBR (pur-