A hormone-independent mouse mammary tumor line was derived by transplantation of a hormone-dependent line (MXT-3590) into ovariectomized-adrenalectomized animals and subsequent transplantation of surviving tumors. Although the tumor line is hormone independent, it contains a full complement of estrogen and progesterone receptors which are similar to those found in hormone-dependent tumors. This similarity includes the criteria of nuclear translocation of the estrogen receptor and subsequent stimulation of progesterone receptor synthesis. In addition to the estrogen receptor, a secondary estrogenbinding site (type II) is also present; this binding site was previously described in the hormone-dependent companion tumor line. Thus, while this variant tumor line contains the biosynthetic pathways that control estrogen and progesterone receptor synthesis, its growth does not depend on these steroids. Therefore, it may provide a good model for the study of this class of hormone-independent tumors.
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