Polyostotic fibrous dysplasia may continue to cause problems into adulthood. If it involves the limb girdles, it can cause crippling deformities and fractures. The McCune-Albright syndrome usually presents with precocious sexual development, most often in girls. The skeletal manifestations are managed as for other polyostotic fibrous dysplasia, whereas the endocrinopathies are treated medically.
Metastatic tumors greatly outnumber primary bone cancers. The pathways of tumor spread to bone include (1) direct extension, (2) lymphatic or hematogenous dissemination, and (3) intraspinal seeding (via the Batson plexus of veins). Any cancer can spread to bone, but in adults more than 75% of skeletal metastases originate from cancers of the prostate, breast, kidney, and lung. In children, metastases to bone originate from neuroblastoma, Wilms tumor, and rhabdomyosarcoma.
Skeletal metastases are typically multifocal and involve the axial skeleton, especially the vertebral column. The radiographic appearance of metastases may be purely lytic (bone destroying), purely blastic (bone forming), or mixed. Bidirectional interactions between metastatic cancer cells and native bone cells account for the changes that manifest in the bone matrix. Tumor cells secrete substances such as prostaglandins, cytokines, and PTH-like peptide that upregulate RANKL on osteoblasts and stromal cells thereby stimulating osteoclast activity. At the same time, tumor cell growth is supported by the release of matrix-bound growth factors (e.g., TGF-β, IGF-1, and FGF) as bone is resorbed. Tumor cells secreting WNT proteins that stimulate osteoblastic bone formation may produce sclerotic metastases.
The presence of bone metastases carries a poor prognosis. Therapeutic options include systemic chemotherapy, radiation, and bisphosphonates. Surgery may be necessary to stabilize pathologic fractures.
Fig.21.31Fibrousdysplasiacomposedofcurvilineartrabeculaeofwovenbonethatlackconspicuousosteoblasticrimmingandariseinabackgroundoffibroustissue.
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Primarybonetumorsareclassifiedaccordingtothecelloforiginorthematrixthattheyproduce.Theremainderisgroupedaccordingtoclinicopathologicfeatures.Mostprimarybonetumorsarebenign.Metastases,especiallyfromlung,prostate,kidneys,andbreast,arefarmorecommonthanprimaryboneneoplasms.
•Boneforming:Osteoblastomaandosteoidosteomaconsistofbenignosteoblaststhatsynthesizeosteoid.Osteosarcoma isanaggressivetumorofmalignantosteoblasts,predominantlyoccurringinadolescents.
Cartilageforming:Osteochondromaisanexostosiswithacartilagecap.SporadicandsyndromicformsarisefrommutationsintheEXT genes.Chondromasarebenigntumorsproducinghyalinecartilage,usuallyarisinginthedigits.Chondrosarcomasaremalignanttumorsofchondroidcellsthatinvolvetheaxialskeletoninadults.
Ewingsarcomasareaggressive,malignant,smallroundcelltumorsmostoftenassociatedwitht(11;22).
Fibrousdysplasiaisanexampleofadisordercausedbygain-of-functionmutationsthatoccurduringdevelopment.