Radiation Therapy (Primary and Recurrent Disease)
Radiation therapy (RT) plays an essential role in the multimodal treatment of all stages of Merkel cell carcinoma (MCC). In this chapter, we review the clinical and laboratory evidence demonstrating the radiosensitivity of MCC, the basis for current treat
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Radiation Therapy (Primary and Recurrent Disease) William R. Silveira and Sue S. Yom
Summary Radiation therapy (RT) plays an essential role in the multimodal treatment of all stages of Merkel cell carcinoma (MCC). In this chapter, we review the evidence demonstrating the radiosensitivity of MCC, the basis for current treatment recommendations for primary MCC, and principles for oncologic decision-making for recurrent and metastatic MCC. Case examples are presented to illustrate the role of RT in management. Evidencebased findings regarding definitive and adjuvant (postoperative) RT are discussed. Finally, future directions and new techniques under development are described.
Introduction The radiosensitivity of MCC was established in the 1980s. Observations regarding the remarkable responsiveness of this tumor type led to RT’s current crucial role in the local and regional control of MCC. Prior to this, treatment had primarily involved wide surgical excision when feasible.
W.R. Silveira (*) • S.S. Yom Department of Radiation Oncology, University of California, San Francisco, 1600 Divisadero Street, Suite H1031, San Francisco, CA 94115, USA e-mail: [email protected]; [email protected]
Cotlar et al. [1] examined eight patients treated initially by surgical resection followed by adjuvant RT and found that the tumor was highly radiosensitive. Despite a successful outcome in just one patient, there was only a single failure within eight irradiated fields. The sensitivity of MCC to radiation was also demonstrated clinically in patients with regional and distant nodal disease. Long-term survival was achieved in one patient with axillary disease treated with postdissection RT to 45 Gy [2]. Raaf et al. conducted a review of the literature including case reports, with conclusions supporting the utility of RT due to the excellent treatment responses of recurrent and metastatic MCC [2]. In another small, early retrospective study examining four patients with MCC, three of them had a complete response to radiation delivered to the primary tumor at a median follow-up of 1.5 years. There was also early evidence that postoperative nodal irradiation provided excellent regional control [3]. In general terms, the response of MCC to radiation is impressive. However, a moderate variation in clinical response has been observed clinically in patients treated for macroscopic disease. This variability has been quantified in MCC cell lines [4]. Experiments show that MCC cell lines produce a range in the surviving fraction at 2 Gy from 0.21 to 0.45 with an average of 0.30, which is very close to that of small cell lung cancer (SCLC). Samples derived from one tumor showed variability in the surviving fraction, supporting the notion that MCC can develop areas of radioresistance.
M. Alam et al. (eds.), Merkel Cell Carcinoma, DOI 10.1007/978-1-4614-6608-6_9, © Springer Science+Business Media New York 2013
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The observed radiosensitivity of MCC in the laboratory and the clinic opened up an opportunity to obviate the need
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