RADIOIMMUNOTHERAPY IN PATIENTS WITH HEAD AND NECK SQUAMOUS CELL CARCINOMA: INITIAL EXPERIENCE David R. Colnot, MD, 1 Jasper J. Quak, MD, PhD, 1 Jan C. Roos, MD, PhD, 2 Remco de Bree, MD, PhD, 1 Abraham J. Wilhelm, MSc, 2 Gordon B. Snow, MD, PhD, 1 Guus A. M. S. van Dongen, PhD 1 1 Department of Otolaryngology-Head and Neck Surgery, University Hospital Vrije Universiteit, De Boelelaan 1117, PO Box 7057, 1007 MB Amsterdam, The Netherlands. E-mail: gams.vandongen@azvu.nl 2 Department of Nuclear Medicine, University Hospital Vrije Universiteit, Amsterdam, The Netherlands Accepted 18 December 2000 Abstract: Background. Despite improvements in locoregional treatment of stages III/IV squamous cell carcinoma of the head and neck (HNSCC), local and distant failure rates remain high. An effective adjuvant therapy is required for these patients. Among novel approaches is radioimmunotherapy, in which monoclonal antibodies (MAbs) are used for selective delivery of radiation to tumor cells. Methods. The suitability of 186 Re-labeled chimeric MAb U36 ( 186 Re-cMAb U36) for radioimmunotherapy was evaluated in a phase I study, with radiation dose escalating steps of 11, 27, and 41 mCi/m 2 . Tumor targeting was monitored with a gamma cam- era, and the maximum tolerated dose was established in 13 pa- tients with recurrent or metastatic disease. Results. Administrations were well tolerated, and excellent targeting of tumor lesions was seen. Myelotoxicity was the only toxicity observed, resulting in dose-limiting toxicity in two patients treated with 41 mCi/m 2 . The MTD was established at 27 mCi/m 2 . A marked reduction in tumor size was observed in two patients, another showed stable disease for 6 months. Conclusions. Radioimmunotherapy with 186 Re-cMAb U36 seems to be well tolerated, with bone marrow being the dose- limiting organ. The observation of antitumor effects is encourag- ing for further development of radioimmunotherapy for HNSCC. © 2001 John Wiley & Sons, Inc. Head Neck 23: 559–565, 2001. Keywords: head and neck cancer; radioimmunotherapy; mono- clonal antibodies Squamous cell carcinoma of the head and neck (HNSCC) accounts for approximately 5% of all newly diagnosed cancers in Europe and the United States. Worldwide, more than 500,000 new cases are diagnosed annually. 1 Despite im- provements in locoregional treatment modalities (ie, surgery and radiotherapy), there is still a high failure rate for stages III/IV, locally as well as at distant sites. Treatment with (neo)adjuvant che- motherapy has failed to improve survival of these patients. 2 An effective adjuvant systemic treat- ment for remaining minimal residual disease is therefore needed to improve survival rates in this patient group. Among the novel approaches for selective systemic treatment is the use of mono- Correspondence to: G. A. M. S. van Dongen Contract grant sponsor: Dutch Cancer Society and Centocor Inc., Mal- vern, Pennsylvania; Contract grant no. VU96-1313. Presented at the 5th International Conference on Head and Neck Cancer, July 29–August 2, 2000, San Francisco, California. © 2001 John Wiley & Sons, Inc. Radioimmunotherapy in Head and Neck Cancer HEAD & NECK July 2001 559