Jawbone Necrosis Affects One in Eight Breast Cancer Patients on Bone Drugs, Finnish Registry Finds

A nationwide Finnish registry study has delivered one of the clearest pictures yet of how often a serious jaw condition strikes women with advanced breast cancer, and the numbers are striking enough to demand attention from oncologists and dentists alike. Researchers at the University of Oulu found that medication-related osteonecrosis of the jaw, a condition in which bone tissue in the jaw dies, was diagnosed during long-term follow-up in 12.6 percent of patients treated with the bone-strengthening drug denosumab. Among patients who had first received bisphosphonates before switching to denosumab, the figure rose to 15.3 percent. Only a small proportion of patients treated with bisphosphonates alone developed the condition. The study, published in the journal Clinical Oral Investigations on 29 September 2026, is the first population-based investigation of this complication among Finnish breast cancer patients whose disease had spread to the bones.

The drugs at the center of the findings, known as antiresorptives, are a cornerstone of modern treatment for bone metastases. Breast cancer that has spread to the skeleton disrupts the normal balance of bone remodeling, tipping it toward excessive breakdown by cells called osteoclasts. This process causes pain, fractures, spinal cord compression and dangerously high calcium levels. Antiresorptive drugs work by suppressing osteoclast activity. Bisphosphonates, such as zoledronic acid, bind to bone mineral and poison the resorption machinery of osteoclasts, while denosumab, a monoclonal antibody, blocks RANKL, the signaling molecule that osteoclasts need to form, function and survive. By dampening bone turnover, these agents reduce skeletal complications and improve quality of life for patients with metastatic disease.

Yet the same mechanism that protects the skeleton carries a paradoxical risk in the jaw. Osteonecrosis of the jaw associated with these medications, abbreviated MRONJ, typically appears as exposed bone in the mouth that fails to heal for more than eight weeks, in patients with no history of radiation therapy to the head or neck. The jawbone is subject to constant mechanical stress from chewing and is frequently challenged by dental infections and procedures. When bone remodeling is profoundly suppressed, the normal repair of tiny injuries in the jaw may be impaired, and dead bone can persist as an open, infection-prone wound. The condition can cause pain, swelling, loose teeth and recurrent infections, and it is notoriously difficult to treat once established.

The Oulu research team designed their study as a retrospective nationwide registry analysis, combining data from the Finnish Institute for Health and Welfare and the Social Insurance Institution of Finland. This approach gave them access to a complete, population-based dataset rather than the selected patient groups seen at single hospitals. The cohort consisted of 652 breast cancer patients with bone metastases who received antiresorptive treatment between 2013 and 2015, and the researchers followed the patients until the end of 2020. That multi-year window matters, because osteonecrosis of the jaw can develop slowly over an extended period, and studies with shorter observation times may substantially underestimate how often it occurs.

The headline figures, 12.6 percent for denosumab alone and 15.3 percent for patients who switched from bisphosphonates to denosumab, are notably higher than many earlier estimates, which often ranged from a few percent in pooled analyses. The Finnish team attributes part of this difference to their long follow-up and their ability to capture diagnoses across the entire national healthcare system. Because the dataset covered all of Finland, the researchers could assess the incidence of the condition and the factors associated with it specifically among Finnish patients with breast cancer that had spread to the bones, something that had never been done before in the country.

Beyond the overall incidence, the study uncovered a telling pattern in the dental records. Dental procedures related to oral infections were associated with the development of osteonecrosis of the jaw. Tooth extraction and root canal treatment, in particular, were linked to a higher risk of the condition. Tooth extraction has long been recognized in the international literature as the most common triggering event for MRONJ, because it creates an open wound in bone whose healing capacity has been chemically dampened. The association with root canal treatment is more novel, but the researchers urge caution in interpreting it: the number of patients in the cohort who underwent root canal treatment was small, and the finding does not establish that the procedure itself causes osteonecrosis of the jaw. It may instead serve as a marker of underlying oral infection or inflammation.

Miika Kujanpää, a doctoral researcher at the University of Oulu, emphasized that the results should not alarm patients into abandoning their cancer treatment. The findings alone do not warrant changing or discontinuing antiresorptive therapy, he noted, and the benefits and potential risks must be assessed on an individual basis. Nor, he stressed, should necessary dental treatment be withheld because of the associations observed. What the results do highlight, according to Kujanpää, is the importance of identifying and adequately treating potential sources of oral infection before starting antiresorptive therapy, and of monitoring oral health continuously throughout the course of treatment. Achieving that, he said, requires close collaboration between oncology and oral healthcare professionals, two specialties that historically have not always coordinated closely.

This preventive message carries real clinical weight. If active infections and non-healing dental problems are resolved before a patient begins denosumab or bisphosphonates, the jaw enters treatment in the best possible condition, with no open wounds to seed necrosis. Once therapy has started, invasive dental work becomes more hazardous, because the suppressed bone turnover persists for months or even years after each dose, particularly with denosumab’s long-acting antibody mechanism. Many international guidelines already recommend a dental examination before initiating antiresorptive therapy, but adherence varies widely, and the Finnish data provide fresh, population-based evidence for why that recommendation matters in everyday oncology practice.

The researchers are careful to frame their study as a beginning rather than an endpoint. They call for further research into how drug dosage, treatment duration and cumulative exposure are associated with osteonecrosis of the jaw, questions that registry data alone cannot fully resolve. More precise information is also needed on the timing of oral infections, dental procedures and the onset of the condition, so that the effects of different contributing factors can be disentangled. And they underline the necessity of sufficiently long follow-up in future studies, since the condition can emerge over an extended period and shorter observation windows risk understating its true incidence.

Perhaps the most consequential question the study raises is also the most practical: how much planned, preventive oral healthcare can actually reduce the risk of osteonecrosis of the jaw? If a structured program of dental screening, infection control and timely treatment before and during antiresorptive therapy can meaningfully lower the incidence observed in Finland, the payoff for patients with metastatic breast cancer could be substantial, sparing them a painful and disabling complication without compromising the bone protection they need. The study was supported by research grants from the Finnish Dental Society Apollonia, and its publication in Clinical Oral Investigations marks a step toward evidence-based, jointly managed care at the intersection of cancer medicine and dentistry. For the hundreds of thousands of women worldwide living with breast cancer that has reached their bones, the message from Finland is clear: the teeth and jaws deserve a place on the treatment plan.

Subject of Research: Incidence and risk factors of medication-related osteonecrosis of the jaw in breast cancer patients with bone metastases receiving antiresorptive treatment

Article Title: Jawbone necrosis in advanced breast cancer: Finnish study highlights the importance of oral health

Article References: Jawbone necrosis in advanced breast cancer: Finnish study highlights the importance of oral health. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: osteonecrosis of the jaw, breast cancer, bone metastases, denosumab, bisphosphonates, antiresorptive drugs, oral health, tooth extraction, registry study, Finland, University of Oulu, Clinical Oral Investigations