Hi Paige,
I don't recall if you previously told us this information or not, but I'm guessing that your vitamin D level may be low. (If so, that's probably a primary reason why you have osteopenia, in the first place - adequate vitamin D is essential for the the body to be able to utilize calcium, in order to create new bone tissue). However, the reason I'm bringing this up, is because of the black box warning that Forteo carries, concerning the risk of osteosarcoma while taking the drug, or afterwards.
Vitamin D is apparently one of the best weapons available, for preventing all types of cancer. Research shows that a high vitamin D level in the blood can definitely offer significant protection against many types of cancer. Therefore, for someone in a relatively high risk situation, such as you are, I would recommend that you do everything you can, to maintain your 25(OH)D level in your blood, at the top of the range, or even above, (at the higher levels, vitamin D can actually have a therapeutic effect). IOW, if I were in your shoes, I would keep it up near 100 ng/mL, or above, (but not above about 150 mg/mL).
Forteo appears to work, but not without risk. Your doctor misinformed you, if he told you that Forteo has no side effects. You can view a list of some of the side effects in the first article referenced below.
The biggest problem, of course, is the black box warning that it carries. In case your doctor didn't discuss that with you, the following articles address it. I'm not trying to scare you, because presumably the risk is relatively low, but osteosarcoma is serious stuff, and the black box warning is there for a reason.
http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0000227
http://www.healthcentral.com/osteoporos ... teo-risks/
The web page referenced below was written for medical professionals, so it contains very comprehensive information about the drug, and related clinical trials:
http://www.drugs.com/pro/forteo.html
If you're going to take Forteo, a high vitamin D level, may be your best friend. Not only will it help to ward off cancer, but it will enhance your ability to build new bone tissue from the calcium in your diet. If you're afraid to take large doses of vitamin D, please at least keep your 25(OH)D level in the upper half of the range, in order to avoid any risk of vitamin D insufficiency.
I wish you the best of luck with this project, and with your MC treatment program.
Tex