We moreover confirmed previous evidence of a net increase
We, moreover, confirmed previous evidence of a net increase of CT density of bone metastases after ZA treatment and demonstrated that the changes persist at a 24 months follow-up. This study and previous reports [24–26] have demonstrated significant sclerotic changes of BMs, more evident in patients with osteolytic lesions. The current data show that changes persist after 24 months of treatment in both osteolytic and osteoblastic metastases. The CT density of osteolytic metastases shows a progressive increase at 24 months in comparison to the 12 months time-point, suggesting that the effect does not reach a plateau level, even after 24 months of treatment. These data support and confirm a cannabinoid receptor effect of ZA as an inhibitor of osteoclastic activity, even in the long-term treatment. Previous reports have shown the effect of concomitant ZA and radiation treatment on density of bone metastases . Radiation therapy alone has been previously shown to increase density of bone metastases by means of quantitative computed tomography [31–33]; in our study, however, skeletal segments previously treated with radiation were not considered and excluded from analysis.
Since concurrent antiblastic and/or hormonal treatments were not discontinued, we cannot rule out an effect on density due to other drugs or to their interactions with ZA. However, bone density increase was seen both in extra-skeletal “responder” and “non-responder” patients, as previously shown . In rat models, ZA alone produces dose-dependent increases in cancellous bone volume and connectivity, 100 times more effectively than pamidronate, and decreases bone resorption . As such, due to the inclusion of patients with different primary tumors and different chemotherapeutic schedules, it is sufficiently safe to claim, on the basis of our and previous reported data, a direct and independent effect of ZA on the increase of density of bone metastases in our patients. This effect is also supported by several reports showing that biphosphonate administration may significantly decrease levels of osteolytic [35,36] and osteoblastic [37,38] bone markers. Moreover, up-regulation of NF-κB ligand (RANKL) and osteoprotegerin levels , critical for the regulation of osteoclasts maturation, function, and survival, are known to occur following biphosphonates treatment [40,41].
Osteosclerosis was also significant at the level of osteoblastic bone metastases. The effect, in this case, seemed to reach a plateau level since the difference between the 24 and the 12 months time point was not significant in this subgroup. Residual osteoclastic activity is present even in sclerotic metastases as it is suggested by some evidence of increased bone resorption in osteosclerotic metastases of prostate cancer [42,43]. Yi et al.  have shown in an animal model of osteoblastic metastases that an initial phase of bone destruction is followed by extensive formation of bone. Their data suggest that bone resorption precedes bone formation in the development of osteoblastic metastases and that osteoclast activation plays an important role even in the course of osteoblastic metastases [44,45]. The plateau of the increment of density, indeed, could be explained either by a minor effect of ZA on osteoblastic metastases or even by the reaching of HU saturation levels.
A limitation of the study is represented by the lack of quantitative computed tomography measurements . Moreover, given the thin thickness of the cortical bone at the femoral neck, analysis at this site may be biased. However, on this regard, our method of analysis can be applied on routine CT images to evaluate responses to ZA therapy in oncologic patients without needs of additional softwares or phantoms. As such, measurements of response to therapy may be conducted in the standard clinical setting without additional tools.
Introduction Evidence-based medicine (EBM) has been defined as the “integration of best research evidence with clinical expertise and patient values”. The first historical descriptions of EBM date back to the beginning of 1990s, when the work of Gordon Guyatt, David Sackett and others established the emerging methodologies of EBM [8,20].