Table 8. Characteristics of Melanocytic Lesions continued...
(Refer to the PDQ summary on adult Skin Cancer Treatment for more information.)
Chordoma is a very rare tumor of bone that arises from remnants of the notochord within the clivus, spinal vertebrae, or sacrum. The incidence in the United States is approximately one case per one million people per year, and only 5% of all chordomas occur in patients younger than 20 years. Most pediatric patients have the conventional or chondroid variant of chordoma.[131,132]
Younger children appear to have a worse outlook than older patients.[131,133,134,135,136] The survival rate in children and adolescents ranges from about 50% to 80%.[131,134,136]
Patients usually present with pain, with or without neurologic deficits such as cranial or other nerve impairment. Diagnosis is straightforward when the typical physaliferous (soap-bubble-bearing) cells are present. Differential diagnosis is sometimes difficult and includes dedifferentiated chordoma and chondrosarcoma. Childhood chordoma has been associated with tuberous sclerosis complex.
Standard treatment includes surgery and external radiation therapy, often proton-beam radiation. Surgery is not commonly curative in children and adolescents because of difficulty obtaining clear margins and the likelihood of the chordoma arising in the skull base, rather than in the sacrum, making them relatively inaccessible to complete surgical excision. The best results have been obtained using proton-beam therapy (charged-particle radiation therapy).[138,139]; [Level of evidence: 3iiA]; [Level of evidence: 3iiiDiii]
There is no known effective cytotoxic agent or combination chemotherapy for this disease, with only anecdotal reports published. Imatinib mesylate has been studied in adults with chordoma on the basis of the overexpression of PDGFR alpha, beta, and KIT in this disease.[141,142] Among 50 adults with chordoma treated with imatinib and evaluable by RECIST, there was one partial response and 28 additional patients had stable disease at 6 months. The low rate of RECIST responses and the potentially slow natural course of the disease complicate the assessment of the efficacy of imatinib for chordoma. Other tyrosine kinase inhibitors and combinations involving kinase inhibitors have been studied.[143,144,145]
Recurrences are usually local but can include distant metastases to lungs or bone.
Cancer of Unknown Primary Site
Cancers of unknown primary site present as a metastatic cancer for which a precise primary tumor site cannot be determined. As an example, lymph nodes at the base of the skull may enlarge in relationship to a tumor that may be on the face or the scalp but is not evident by physical examination or by radiographic imaging. Thus, modern imaging techniques may indicate the extent of the disease but not a primary site. Tumors such as adenocarcinomas, melanomas, and embryonal tumors such as rhabdomyosarcomas and neuroblastomas may have the above-mentioned presentation. Children represent less than 1% of all solid cancers of unknown primary site and because of the age-related incidence of tumor types, embryonal histologies are more common in this age group.