There is a controversy regarding the prognosis of the progesterone receptor (PR) isoform ratio in luminal breast cancer. We suggested that excess in isoform B over isoform A of PR (PRB-H tumors) is associated with the luminal B subtype. Thus, patients with PRB-H tumors would have lower survival compared with PRA-H patients. This study aimed to compare the metastatic and proliferative patterns of a PRA-H murine antiprogestin-sensitive tumor (C7-2-HI) with its antiprogestin-resistant PRB-H variant (C7-2-HIR) and to search candidates to decipher their biological behavior. Two approaches were performed. To test early metastases, tumors were inoculated subcutaneously in BALB/c mice and euthanized after 42 days (n=7-8/group). Lungs were histologically examined. A higher number of foci were generated by the PRA-H tumor compared to the PRB-H counterpart (Mann-Whitney, p<0.01), regardless that the proliferation rate of the former was almost twice lower than the latter (linear regression, p<0.01). In the late metastases setting surgery was performed in both groups (n=5-8/group) at similar tumor sizes, and lungs were examined after 90 days. The PRA-H model generated several lung foci, and in the PRB-H model, there were either none or few huge foci (p 1 and FDR < 0.05) compared to the PRB-H variant. These results confirm that when PRA-H tumors progress to a PRB-H phenotype there is an increase in the proliferative state in detriment of the metastatic ability. Depending on the metastatic spread before surgery, PRA-H tumors may have an increased number of foci than PRB-H tumors, but they might grow very slowly. On the contrary, the PRB-H metastasis may grow so fast that may affect normal organ function in a shorter time.