Ewing sarcoma : treatment, prognosis and late effects

Abstract: Ewing sarcoma (ES) is a rare and aggressive childhood/adolescent malignancy which relies on a multidisciplinary treatment approach for cure. The overall survival rate for this young patient group has hardly improved over the last 30 years despite large multinational treatment trials. Thus, there are important research questions to be answered with regards to systemic treatment. However, this thesis is about local treatment. Local treatment is indisputably important for overall survival, yet we have not reached a consensus for which local treatment regime is best for the individual patient. Therefore, local treatment is always a matter of debate on multidisciplinary meetings in sarcoma centers around the world. In the national multidisciplinary sarcoma conferences hosted at the Karolinska University Hospital every fortnight, every ES case in the country is brought up for discussion and there is an unproportioned amount of time spent on each case compared to other sarcomas. Due to the rare nature of this disease, randomized trials on local treatment are unlikely to occur and local treatment relies on case series and studies hampered by low number of patients. This thesis aims to shed light on the following questions: (1) which is the optimal local treatment strategy for pelvic ES; (2) how are ES of the spine treated in Scandinavia and what is the neurologic and oncologic outcome; (3) what is the true risk for subsequent primary neoplasms (SPNs) among ES survivors and (4) what is the effect of local treatment on local failure, long term mortality and morbidity? Study 1 evaluates different local treatment options in treatment of pelvic ES and whether local control of sacral ES can be achieved with radiotherapy alone. Innominate bone ES were in most cases treated surgically and sacral bone tumors were largely treated with radiotherapy (RT) alone. We found that sacral site was an independently favorable site as regards disease- free survival compared with the innominate bones. Furthermore, good local control could be obtained with RT alone for tumors located in the sacrum. Study 2 investigated if the same good outcome found among ES of the sacrum could be seen among patients with ES of the mobile spine. Additionally, the neurologic deficits at time of diagnosis and at end of follow-up for ES of the mobile spine were examined in relation to local treatment. Only 24 patients with sufficient data were found eligible for the analysis. Neurologic deficits at presentation were common which often led to emergency decompression before having a histopathologic diagnosis. Emergency decompression was associated with a higher rate of local failure. Most patients recovered neurologically regardless of local treatment, perhaps because of prompt initiation of systemic treatment leading to tumor shrinkage and less pressure on the spinal cord. Disease-free survival was relatively favorable, but perhaps not as good as that of sacral ES. As was the case with sacral ES, the majority of patient were treated with RT exclusively which reflects the difficulties in performing “en bloc” surgery in this site. Local control was excellent for the few patients with tumors manageable by surgery. Study 3 investigated the risk for secondary malignancies among Ewing- and osteosarcoma (OS) survivors in a population-based nationwide cohort. ES survivors had double the risk of OS survivors, and a four times higher risk than the general population of acquiring an SPN. The excess risk was largely driven by breast cancer and female genital malignancies for ES as well as OS survivors, and not as much by secondary sarcoma as anticipated. Due to the high background breast cancer incidence in the general population, the excess breast cancer risk among ES survivors translates to 127 extra breast cancers per 10 000 person years. The excess cancer risk remained elevated with increasing follow-up and over calendar time. Study 4 evaluated the role of surgery and RT in relation to surgical margin and local control. Secondarily, the effect of local treatment on long-term mortality, occurrence of SPN and hospitalization was studied. Local treatment had a significant effect not only on local failure, but also on overall survival. Surgical treatment gave superior local control compared with definitive RT. The lowest local failure rate was achieved if surgery was performed with a wide surgical margin. Nonetheless, RT also played a significant role with regards to local control since marginally resected tumors treated with adjuvant RT achieved an equal local control rate to that of a wide margin. This is a key finding because accomplishing a wide surgical margin is rarely possible for tumors located in the pelvis or spine, sites which comprise a third of all ES. In conclusion, tumor site is an important prognostic factor in ES. Pelvic and spinal sites pose a specific challenge since surgery of the primary tumor is less often performed due to the morbidity associated with surgery in these sites. Hence, more patients will receive definitive RT. Definitive RT seems to achieve good local control for tumors of the sacrum. Nevertheless, the long-term results of definitive RT are unknown. For tumors located in sites other than the sacrum, surgery is superior to definitive RT in achieving local control and improving survival. Moreover, best local control is achieved when surgery is carried out with wide margins, in which case RT does not improve outcome. Importantly, radiotherapy improves local control for marginally resected tumors. The long-term excess risks for SPNs are mainly driven by breast cancer among females. Unfortunately, the risks remain high in recent treatment periods. Moreover, the excess risk persists with extended follow-up, indicating the need for lifelong surveillance and tailored follow-up. However, the outcome after local recurrence is dismal. The benefit of administering RT when indicated must therefore not be overshadowed by the risk for treatment related cancer.