Inactivating mutations in NF1 underlie the prevalent familial cancer syndrome neurofibromatosis type 1 [1]. The NF1-encoded protein is a Ras GTPase-activating protein (RasGAP) [2]. Accordingly, Ras is aberrantly activated in NF1-deficient tumors; however, it is unknown which effector pathways critically function in tumor development. Here we provide in vivo evidence that TORC1/mTOR activity is essential for tumorigenesis. Specifically, we show that the mTOR inhibitor rapamycin potently suppresses the growth of aggressive NF1-associated malignancies in a genetically engineered murine model. However, in these tumors rapamycin does not function via mechanisms generally assumed to mediate tumor suppression, including inhibition of HIF-1alpha and indirect suppression of AKT, but does suppress the mTOR target Cyclin D1 [3]. These results demonstrate that mTOR inhibitors may be an effective targeted therapy for this commonly untreatable malignancy. Moreover, they indicate that mTOR inhibitors do not suppress all tumor types via the same mechanism, suggesting that current biomarkers that rely on HIF-1alpha suppression may not be informative for all cancers. Finally, our results reveal important differences between the effects of mTOR inhibition on the microvasculature in genetically engineered versus xenograft models and indicate that the former may be required for effective preclinical screening with this class of inhibitors.

Objective:To determine the treatment outcome and prognostic factors in patients with adenoid cystic carcinoma of the skull base treated with proton beam radiation therapy.Design: Retrospective analysis.Setting: Massachusetts General Hospital, Massachusetts Eye and Ear Infirmary, and Harvard Medical School, Boston.Patients: From 1991 to 2002, 23 patients with newly diagnosed adenoid cystic carcinoma with skull base extension were treated with combined proton and photon radiotherapy. There was tumor involvement of the sphenoid sinus in 61% of patients (14), nasopharynx in 61% (14), clivus in 48% (11), and cavernous sinus in 74% (17). The extent of surgery was biopsy alone in 48% (11), partial resection in 39% (9), and gross total resection with positive margins in 13% (3). The median total dose to the primary site was 75.9 cobalt-gray equivalent. The median follow-up of all surviving patients was 64 months. Main Outcome Measures:Locoregional control and disease-free survival and overall survival rates.Results: Tumors recurred locally in 2 patients at 33 and 68 months, respectively. No patients developed neck recurrence. Eight patients had distant metastasis as the first site of recurrence. The local control rate at 5 years was 93%. The rate of freedom from distant metastasis at 5 years was 62%. The disease-free and overall survival rates at 5 years were 56% and 77%, respectively. In multivariate analysis, significant adverse factors predictive for overall survival were change in vision at presentation (P=.02) and involvement of sphenoid sinus and clivus (P=.01). Conclusions:High-dose conformal proton beam radiation therapy results in a very encouraging local control rate in patients with adenoid cystic carcinoma of the skull base. Changes in vision at presentation and tumor involvement of the sphenoid sinus and clivus are important prognostic factors.

Late relapse is common among adult patients with medulloblastomas, and long-term follow-up monitoring is important. Because of the high risk of systemic failure among the low-risk patients treated with radiotherapy alone, the role of chemotherapy for this group of patients needs to be further investigated. Complete resection, the absence of brainstem invasion, and an overall radiotherapy duration of less than 48 days are important prognostic factors.