A 15-year-old girl is being evaluated for a thyroid nodule. Her family history is significant for her father and older sister having undergone prophylactic thyroidectomies. Genetic testing confirms she has a pathogenic variant in the RET proto-oncogene consistent with multiple endocrine neoplasia type 2b. In addition to a near-certain lifetime risk of medullary thyroid carcinoma, which other malignancy is she at high risk of developing?