Tamoxifen and Exemestane Trial Bone Substudy - A substudy to Amendment 2 of the IBCSG 25-02 / BIG 3-02: Tamoxifen and Exemestane Trial (ACTRN12605000418673) hereby referred to as TEXT-2, which evaluates the effects of exemestane plus Gonadotropin-releasing hormone (GnRH) analogue as adjuvant therapy for premenopausal women with endocrine responsive breast cancer

Prior to registration in the TEXT-Bone Substudy, patients must be randomised to the TEXT-2 parent trial (Protocol Amendment 2 of IBCSG 25-02 / BIG 3-02 Tamoxifen and Exemestane Trial - TEXT). TEXT-2 re-starts recruitment. The TEXT trial will evaluate the worth of ovarian function suppression (achieved by long-term use of Gonadotropin-releasing hormone (GnRH) analogue (Triptorelin) 3.75mg by intramuscular injection every 28 days for 5 years from randomisation) plus exemestane 25mg orally daily until 5 years from date of randomisation (Exemestane should start after adjuvant chemotherapy has been completed or approximately six to eight weeks after the initiation of Gonadotropin-releasing hormone (GnRH) analogue (Triptorelin) whichever is later) compared with Gonadotropin-releasing hormone (GnRH) analogue (Triptorelin) 3.75mg by intramuscular injection every 28 days for 5 years from randomisation plus tamoxifen 20mg orally daily until 5 years from date of randomisation (Tamoxifen should start after adjuvant chemotherapy has been completed or approximatley six weeks to eight weeks after the initiation of Gonadotropin-releasing hormone (GnRH) analogue (Triptorelin), whichever is later) for premenopausal women with steroid hormone receptor positive early invasive breast cancer. Patients may either receive no chemotherapy or commence chemotherapy at the same time that Gonadotropin-releasing hormone (GnRH)analogue is initiated. Women will be randomised in a 2-arm design to receive one of the following: a. Ovarian Function Suppression (triptorelin) + Tamoxifen b. Ovarian Function Suppression (triptorelin) + Exemestane All treatment will be for 5 years.