For optimal effect Zometa for metastatic bones must be started before pain sets in
 

The results of the study below on Zometa for metastatic bones (to delay &/or reduce pain & reduce the risk of various bone damages) indicate that if Zometa is given before bone pain sets in benefits are superior to those afforded by the competing Pamidronate drug.
Assuming that in spite of the fact that the study was paid by the manufacturer of Zometa, there was no bias to enhance sales, the recommandation to start Zometa early is not currently followed by all oncs.
I think a number of them only prescribe it once pain becomes a QOL matter.
I do not know why this is so except it is perhaps related to former retrospective statistical number crunching of clinical trials which did not demonstrate an improvement in overall survival due to Zometa. An other factor might be the increased awarness of the risk of jaw bone necrosis holding up the decision of some oncs until the risk/reward ratio appears more favorable.

Although I do not have conclusive scientific data to support my hunch, I would prefer early use of Zometa concurrently with Aromatase inhibitors not only to prevent bone fractures but also to delay if not prevent cancer progression.
I base my assumptions on the fact that Zometa has been shown to reduce VEGF in humans(see ref. below) & also on a single anecdotic case I have already described elsewhere: Zometa given alone (after stopping Femara due to excessive osteoporosis) kept for 18 months markers at the best low levels achieved by Femara & kept the patient free of metastases.

http://www.docguide.com/news/content...2571FD004B37B1
Early Zoledronic Benefits Breast Cancer Patients With Bone Metastases But No Bone Pain: Presented At ESMO

Ref
http://clincancerres.aacrjournals.or...tract/9/8/2893
Zoledronic Acid Induces Significant and Long-Lasting Modifications of Circulating Angiogenic Factors in Cancer Patients

http://www.cancereducation.com/Cance...aare/aare1.pdf
Anti-tumor Potential of Bisphosphonates

In my previous post I forgot to mention an other uncertainty about Zometa (& other drugs in the same class of bisphosphonates) which makes some oncs leery to prescribe it in frequent doses for extended periods of time: no one is sure how long the drug stays in the bones but it is probably measured in years if not permanently.

Zometa does not reestablish the normal process of bone resorption & bone formation upset by bone cancer which is described as follows:
"Bisphosphonates inhibit the activity of bone-destroying cells called osteoclasts. Normally, osteoclasts work in harmony with bone-forming cells called osteoblasts in order to rebuild areas of bone that need replacing."

As a result there is uncertainty about the long term quality of bones laced with long lasting bisphosphonates even if they reduce initially the risk of fractures.
This is why Zometa is not yet approved in several countries for osteoporosis.