[Dynseli]

This is because, according to "Hormone Action in the Mammary Gland" they synergize, they boast each other's response. Generally speaking, weak antagonists upregulate that receptor. Fortunately, with breast development there are three hormones that cause growth, and while weak amounts downregulate their own receptor, they upregulate the other two receptors.

As for androgens, androgens possibly upregulate while inhibiting growth. Meaning no to little growth (According to Yen & Jaffe's Reproductive Endocrinology (Sixth Edition): The Breast, the existence of androgens or their receptors were also required for mammary development). DHT inhibits growth and downregulates PR, ER and PrlR.