Screening Trial for Pain Relief in Schwannomatosis (STARFISH)

Inclusion Criteria for Master Study: * Patients must have a confirmed diagnosis schwannomatosis by fulfilling either clinical or molecular diagnosis. * Clinical diagnosis: A clinical diagnosis of schwannomatosis is confirmed by either of the two following criteria: * Two or more non-intradermal schwannomas, one with pathological confirmation, without evidence of bilateral vestibular schwannoma (see exclusion criteria 3.2.3) OR * one pathologically confirmed schwannoma or intracranial meningioma and * An affected first-degree relative. Molecular diagnosis * A molecular diagnosis of schwannomatosis is confirmed by either (1) two or more pathologically proven schwannomas or meningiomas AND genetic studies of at least two tumors with loss of heterozygosity (LOH) for chromosome 22 and two different NF2 mutations; or (2) one pathologically proven schwannoma or meningioma and a germline SMARCB1 or LZTR1 pathogenic mutation. * Participant must be ≥ 18 years of age on Day 1 of treatment. * Karnofsky performance status ≥ 70 or ECOG PS 0 or 1 (see Appendix A). * Subject must have moderate-to-severe pain secondary to SWN, defined as Score ≥5 on the Numeric Rating Scale-11 (NRS-11) as the maximum pain intensity in the previous 7 days. * Ability to understand and the willingness to sign written informed consent and assent documents. * Must have established relationship with primary care physician and provide contact information. Inclusion Criteria for Sub-study A - Siltuximab or P…