A PSA at 45 is considered high (normal is up to 4). Your Gleason score of 4+3=7 is for an intermediate risk but the grade of 4 is for an aggressive type of cancer. These data with 12 cores (biopsy) positive and voluminous involvement is indicative that you got an advanced case of prostate cancer. Nevertheless, you are not alone. There are many guys in similar situation and even with must higher PSA levels, but have done well with treatments.
Other elements are important to understand better your status. The clinical stage would inform about the advancement (contained, localized, metastasized, etc.). Any symptom that made you to check for cancer or DRE are also elements that you will need to make a decision on a treatment. Your age and any other illness will weigh in your case too.
The bone scan will give you more details on the advancement of your case. An endorectal MRI would be helpful to give you an anatomical image of the areas around the prostate and check for localized metastases.
I recommend you to read books on prostate cancer and research in the net typing this sentence; “treatments for prostate cancer”. You should also be aware of the risks and side effects related to each type of treatment.
Here is a good book that may help in preparing a list of questions to your next doctors visit and to understand some comments from your doctor;
"100 QUESTIONS & ANSWERS ABOUT PROSTATE CANCER"; by Alan J. Wein and Pamela Ellsworth.
Welcome to the board.