Insufficient bilateral femoral subtrochanteric fractures in a patient receiving imatinib mesylate

Bone Nanomechanical Properties and Relationship to Bone Turnover and Architecture in Patients With Atypical Femur Fractures: A Prospective Nested Case-Control Study

Atypical femur fractures (AFFs) are well‐established serious complication of long‐term bisphosphonate and denosumab therapy in patients with osteopenia or osteoporosis. To elucidate underlying mechanism(s) for the development of AFF, we performed a nested case‐control study to investigate bone tissue nanomechanical properties and prevailing bone microstructure and tissue‐level remodeling status as assessed by bone histomorphometry. We hypothesized that there would be differences in nanomechanical properties between patients with and without AFF and that bone microstructure and remodeling would be related to nanomechanical properties. Thirty‐two full‐thickness transiliac bone biopsies were obtained from age‐ and sex‐matched patients on long‐term bisphosphonate therapy with (n = 16) and without an AFF (n = 16). Standard histomorphometric measurements were made in each sample on three different bone envelopes (cancellous, intracortical, and endosteal). Iliac bone wall thickness was significantly lower on all three bone surfaces in patients with AFF than in those without AFF. Surface‐based bone formation rate was suppressed similarly in both groups in comparison to healthy premenopausal and postmenopausal women, with no significant difference between the two groups. Nanoindentation was used to assess material properties of cortical and cancellous bone separately. Elastic modulus was higher in cortical than in cancellous bone in patients with AFF as well as compared to the elastic modulus of cortical bone from non‐AFF patients. However, the elastic modulus of the cancellous bone was not different between AFF and non‐AFF groups or between cortical and cancellous bone of non‐AFF patients. Resistance to plastic deformation was decreased in cortical bone in both AFF and non‐AFF groups compared to cancellous bone, but to a greater extent in AFF patients. We conclude that long‐term bisphosphonate therapy is associated with prolonged suppression of bone turnover resulting in altered cortical remodeling and tissue nanomechanical properties leading to AFF. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Osteopenia and fractures associated with long-term therapy with MEK inhibitors

Targeted therapies have markedly improved the survival of patients with melanoma. We report the case of two patients with advanced melanoma controlled by long-term MEK inhibitor or combination of BRAF and MEK inhibitors, who developed fractures related to severe osteopenia. A 48-year-old woman was treated by pimasertib after the failure of two lines of chemotherapy, and a 42-year-old man was treated by an association of BRAFi (dabrafenib) and MEKi (trametinib) after the failure of one line of chemotherapy. During follow-up, both complained of buttock pain, revealing primary fractures of the pelvis and lumbar vertebra. In both patients, none had osteoporosis risk factors; DEXA scan revealed osteopenia, and analysis ruled out metastatic bone lesion or secondary osteoporosis. Zoledronic acid, cholecalciferol (vitamin D3), oral calcium, and pain killers were introduced, leading to no further bone event. Numerous pathways are involved in the homeostasis of bone turnover, and the effect of tyrosine kinase inhibitors on those pathways is not well known yet. The absence of usual causes of osteoporosis or metastatic bone lesion and kinetics of symptoms lead us to suggest that MEK inhibitors were responsible for the development of osteoporosis. To the best of our knowledge, this is the first report of fractures associated with osteopenia in patients treated with MEKi. Long-term survival owing to new targeted treatment could be associated with yet underestimated adverse effects such as osteopenia/osteoporosis that could impair patient's quality of life and should be investigated.

Effects of tyrosine kinase inhibition on bone metabolism: untargeted consequences of targeted therapies

Tyrosine kinase inhibitors (TKIs) are at the forefront of molecular-targeted therapies for cancer. With the advent of imatinib for the treatment of chronic myelogenous leukemia, a new wave of small-molecule therapeutics redefined the oncologic treatment to become chronically administered medications with tolerable side-effect profiles compared with cytotoxic agents. Effects on bone mineral metabolism were observed during early imatinib treatment, in the form of hypophosphatemia with increased urinary phosphorus excretion. This finding led to detailed investigations of off-target effects responsible for changes in bone cell maturation, activity, and impact on bone mass. Subsequently, another BCR-Abl inhibitor (dasatinib), vascular endothelial growth factor (VEGF) inhibitors (sorafenib and sunitinib) as well as rearranged during transfection (RET) inhibitors (vandetanib and cabozantinib) were developed. Inhibition of bone resorption appears to be a class effect and is likely contributed by TKI effects on the hematopoietic and mesenchymal stem cells. As long-term, prospective, clinical outcomes data accumulate on these targeted therapies, the full extent of off-target side effects on bone health will need to be considered along with the significant benefits of tyrosine kinase inhibition in oncologic treatment.

Effect of long term imatinib on bone in adults with chronic myelogenous leukemia and gastrointestinal stromal tumors

Patients with chronic myelogenous leukemia (CML) or gastrointestinal stromal tumors (GIST) who take imatinib have abnormalities of bone metabolism. However, it is unclear what impact these changes have on bone mineral density (BMD). We prospectively analayzed levels of osteocalcin, a marker of bone formation secreted by osteoblasts, and serum N-telopeptide of type I collagen (NTX), a marker of bone resorption, as well as other minerals involved in bone metabolism in 19 patients with either CML or GIST We correlated these results with changes in bone mineral density as measured by serial dual energy X-ray absorptiometry (DEXA) scans over a two year period. Osteocalcin levels were low in 95% of patients and 37% had no measurable amount. Levels of NTX were less consistent. Nine patients (47%) had a decrease in BMD, four patients (2%) had an increase in BMD, and six patients (32%) had no change. There was no correlation between metabolic markers and change in BMD. We suggest that ongoing management of patients who take imatinib should include monitoring of bone health on a long term basis.

Digital image analysis as a tool to assess the effects of imatinib on trabecular bone in patients with chronic myelogenous leukemia

Skeletal integrity is sustained by osteoblast-osteoclast interactions, controlled by several signaling pathways that include tyrosine kinases. Imatinib is a tyrosine kinase inhibitor with an extended therapeutic range based on its ability to differentially bind to receptor and nonreceptor tyrosine kinases. In this study, we used digital image analysis to assess changes in trabecular bone surface area within bone marrow biopsy specimens of 34 patients with chronic phase chronic myelogenous leukemia treated with single-agent imatinib. These patients were 25 men and 9 women with a median age of 59 years. We selected representative areas of paired bone marrow biopsy specimens obtained at baseline and within the subsequent 48 months. Computer-assisted analysis was performed to calculate trabecular bone area (TBA) within the sample by using the equation TBA% = sum of trabecular area/total biopsy specimen area. Percentage changes were defined as ΔTBA% and were arbitrarily subdivided into marked (>50%), moderate (10%-50%), and mild (<10%). During the study interval, TBA% increased in 24 patients (71%) and decreased in 10 patients (29%). Overall, there was a significant increase in TBA% (P = .02). No correlation was found between changes in trabecular bone area and either clinical or cytogenetic response (P = .25). The results show that imatinib therapy can alter trabecular bone in bone marrow biopsy specimens of chronic myelogenous leukemia patients, most often resulting in an increase in TBA%.

Atypical fractures and bisphosphonate therapy: a cohort study of patients with femoral fracture with radiographic adjudication of fracture site and features

Atypical subtrochanteric/femoral shaft (ST/FS) fractures are increasingly reported in patients on long-term treatment with bisphosphonates (BPs). We estimated the frequency of atypical fractures and their association to BP use in patients aged ≥ 50 years consecutively admitted to a single center with a new femoral fracture. All individual radiographs were examined and fracture site confirmed. A case-control study of patients with low-energy ST/FS fractures, age- and sex-matched with patients with hip fractures (1:2 ratio), was performed. Patients with atypical ST/FS fractures were further compared with those with ordinary ST/FS fractures. Cortical thickness (CT) was measured in radiographs of cases and controls. Ninety-six of 906 patients (10.6%) had a ST/FS fracture. Of these, 63 with low-energy fractures were individually matched with 126 controls with hip fracture. BPs were used by 9.5% of cases and by 8.7% of controls (OR, 1.10; 95% CI, 0.39-3.06) with comparable duration of therapy between groups (54 ± 35 vs. 54 ± 52 months, P=0.53). CT was comparable between cases and controls, BP users and non-users, and was not related to treatment duration. Atypical fractures were observed in 10/63 ST/FS cases (15.9%). Compared to patients with ordinary ST/FS fractures, those with atypical fractures were using more frequently BPs (OR, 17.0; 95% CI, 2.6-113.3) and glucocorticoids (OR, 5.3; 95% CI, 0.9-28.6). Among patients with atypical fractures, CT was comparable between BP users and non-users. In conclusion, atypical femoral fractures have a low prevalence (1.1% of all femoral fractures), compared to ordinary ST/FS fractures are more frequent in bisphosphonate users, but equally occur in patients never treated with bisphosphonates.