 A treatment course will consist of 4 weeks of therapy. For stratum 1 treatment may continue until disease progression or unacceptable toxicity occurs. Patients entered on stratum 2 may receive up to a maximum of 6 courses i.e. 24 weeks of therapy unless there is evidence of objective radiographic response, as defined in Section 13.0 to 20 decrease in PN volume, tumor progression, or unacceptable toxicity. Patients who experience unacceptable toxicity or disease progression will be removed from treatment with sirolimus. Patients with documented radiographic response may continue treatment with sirolimus for up to 6 treatment courses after the maximum response. 