A Survival Score for Patients Receiving Stereotactic Radiosurgery Alone for Brain Metastases from Breast Cancer

Discussion

Since the locoregional treatment of breast cancer has considerably improved in recent decades, more patients live longer and, therefore, are more likely to experience metastatic spread during the course of their cancer (12-14). This also applies to the development of brain metastases. Different treatment modalities are available, most of all radiotherapy including WBI with/without SRS. The use of SRS is generally limited to a few, generally three or four cerebral lesions (3). The optimal treatment approach for these patients still requires further research. One question that still needs to be answered is the use of SRS alone or in combination with WBI. A few studies including randomized trials have demonstrated that the addition of WBI to SRS improves local control of the treated lesions, provides freedom from new cerebral lesions, and overall intracerebral control (4-6). However, survival was not improved when WBI was added. Additionally, randomized trials have shown that the risk of decline in neurocognitive function significantly increases with the addition of WBI (7). Therefore, many treating physicians are hesitant regarding the combination of SRS and WBI, and SRS alone is becoming more frequently employed.

If SRS alone is chosen, physicians wish to deliver an individualized treatment approach that optimally meets a patient's individual needs. It is well known that such personalized approaches must take into account a patient's remaining lifespan to optimally balance several important factors, including efficacy of the treatment, treatment-related toxicities, and the burden of treatment for the patient. Therefore, survival scores have gained importance in recent years (15). Because every tumor entity has its specific characteristics, including tumor biology and the pattern of spread, it is important to have available specific scores for each tumor entity. To avoid a selection bias caused by the treatment approach (WBI alone, SRS alone, WBI plus SRS, neurosurgery alone, neurosurgery plus WBI), separate scores should ideally be developed in patient cohorts uniformly treated with one form of treatment (2, 11). Therefore, this study focused solely on patients with one to three brain metastases from breast cancer treated with SRS alone.

Three factors were identified that had a significant impact on survival in such patients, the Karnofsky performance score, the maximum diameter of all cerebral lesions and the presence or not of extracerebral metastases. Based on these factors, three survival groups were defined with significantly different 1-and 2-year survival rates. Patients with 0-1 points had the worst prognosis, with 1-year and 2-year survival rates of 48% and 0%, respectively. In this group, 15 patients died during the follow-up, seven patients from new distant brain metastases and eight patients from extracerebral tumor progression. Therefore, these types of patients would appear to benefit from intensification of systemic treatment in a timely manner. Patients with 2 points by this new score had a more favourable prognosis, with a survival rate of 71% at 1 year and 2 years. Two patients died during follow-up, one patient each from new distant brain metastases and from extracerebral progression. Therefore, such patients may not require WBI in addition to SRS, and systemic treatment should be balanced against potential risks of significant toxicities. Since all of the patients with 3 points were still alive 2 years following SRS without progression of disease, such patients should not receive WBI, and systemic treatment may be withheld until extracerebral progression of disease is detected. Close follow-up, particularly of these patients, is recommended.

In summary, the new survival score developed in this study for patients with breast cancer receiving SRS alone for few brain metastases contributes to the selection of individualized treatment approaches and personalized cancer care of this patient group.