Features of Bone Metastases Associated With Survival Benefit of Radiotherapy for Metastatic Prostate Cancer

The bone metastasis count and location of lesions identified via conventional imaging were found to be tied to overall survival (OS) and failure-free survival (FFS) benefits of prostate radiotherapy for patients with newly diagnosed metastatic disease, according to data published in JAMA Oncology.

The data from this exploratory analysis of the randomized STAMPEDE trial (NCT00268476) regarding bone metastatic burden and metastasis location may help predict survival benefits from prostate radiotherapy for this patient subset.

“Bone metastatic burden based on conventional imaging is predictive of OS and FFS benefit when prostate radiotherapy is added to SOC [standard of care] in newly diagnosed mPC [metastatic prostate cancer],” wrote the investigators. “This beneficial effect is most pronounced in patients with up to 3 bone metastases, below which addition of prostate radiotherapy to SOC improves survival in patients without visceral or other metastasis.”

The survival benefit was strongest up to 3 bone metastases, with survival continuously decreasing as the number of bone metastases increased.

More, subgroup analyses found that the magnitude of benefit for patients when prostate radiotherapy was added was greater for patients with low metastatic burden with only nonregional lymph nodes (M1a) or 3 or fewer bone metastases without visceral metastasis for both OS (HR, 0.62; 95% CI, 0.46-0.83) and FFS (HR, 0.57; 95% CI, 0.47-0.70) than for patients. This compared favorably with patients who has 4 or more bone metastases or any visceral or other metastasis in terms of both OS (HR, 1.08; 95% CI, 0.91-1.28; interaction P = .003) and FFS (HR, 0.87; 95% CI, 0.76-0.99; interaction P = .002). The patients who experienced a greater magnitude of benefit also had low metastatic burden and only nonregional lymph nodes.

The analysis encompassed 1939 men, with a median age of 68 years (interquartile range [IQR], 63-73 years). Of that population, 1732 men had bone metastases.

“These results have established a broad consensus for addition of prostate radiotherapy to standard of care for first-line treatment in men with newly diagnosed, low-metastatic-burden disease,” wrote the investigators. “However, controversy exists on how to define low metastatic burden.”

The primary end points for this research were OS and FFS in this cohort of patients.

While data regarding bone metastatic burden were available for most patients, the research team explained that patients were excluded due to the inability to centralize their scans. More, there was a lack of information regarding quantitative lymph nodes and visceral metastasis, limiting the investigative team’s knowledge of its predictive abilities.

Looking ahead, the researcher team suggests examining newer sensitive imaging modalities, with similar studies used to investigate the clinical relevance relative to utility in predicting treatment outcome.

“The criteria for low metastatic burden based on conventional imaging, predictive of survival benefit from prostate radiotherapy in men with newly diagnosed mPC, should now also include men with M1a disease,” wrote the investigators.

Reference:

Ali A, Hoyle A, Haram AM, et al. Association of bone metastatic burden with survival benefit from prostate radiotherapy in patients with newly diagnosed metastatic prostate cancer. JAMA Oncol. February 18, 2021. doi:10.1001/jamaoncol.2020.7857