Steroid hormone receptors and response to high-dose medroxyprogesterone acetate in advanced breast cancer

Forty-six patients with advanced breast cancer were treated with oral high-dose medroxyprogesterone acetate (MPA) as a second line endocrine treatment, with a 28% 13/46) response rate. There was a significant difference in response to MPA between patients with estrogen (ER)- or progesterone (PgR)-receptors and those with negative receptors assayed just before the treatment (ER+, 7/10, ER-, 0/9 of response rates, p = 0.007, PgR+, 4/4: PgR-, 3/15, p = 0.02). The combination of ER and PgR was observed to be best in predicting the response (p = 0.02). The ER status as well as the combination of ER and PgR, but not PgR alone detected in the primary tumors, correlated well with the response (ER+, 10/23: ER-, 0/15, p = 0.0094, PgR+: PgR-, p = 0.13, ER+PgR+, ER+PgR-, ER-PgR-:p = 0.024). The correlation between steroid hormone receptors and response to MPA in advanced breast cancer was established from the literature. Response rate to MPA was shown to be 42% (69/169) in ER+ cancer patients, and 10% (9/90) in ER- cancer patients (p = 0.00004). There was no correlation between PgR status and the response. Changes of receptors were studied in relation to the response. When ER+ or PgR+ tumors retained their positivity until MPA treatment, a good response was obtained, while there were almost no responders if one or both receptors changed from positive to negative, or remained negative. In conclusion, the response to MPA can be predicted by the steroid hormone receptors.