Epidemiology of primary bone tumors and economical aspects of bone metastases

Acknowledgments

The authors are indebted to Prof. E Hauben for involvement in the previous version of this book chapter.

Primary bone tumors are rare and as such they form a difficult category of tumors for appropriate recognition and classification both for treating clinicians as well as radiologists and pathologists. They account for less than 0.2% of the malignancies registered in the SEER database [ ]. The occurrence of bone sarcomas ranges between 0.8 and 2 cases per person per year [ ]. As compared to soft tissue sarcomas, bone sarcomas are about one-tenth of the incidence of their soft tissue counterparts [ ]. The most common primary bone sarcomas are osteosarcoma, chondrosarcoma, Ewing sarcoma, and undifferentiated pleomorphic sarcoma, previously known as MFH of bone. However, particularly children and adolescents are affected which make those bone tumors have a major impact on life of the patients and his/her immediate surroundings. The incidence of benign bone tumors is considerably higher. A number of them, however, are asymptomatic and therefore do not draw to the patient's and doctor's attention. Therefore benign bone tumors most likely are underreported but nevertheless they are as compared to other benign tumors occurring in the body as rare event. Another confounding factor is the high discrepancy rate at histological review of bone tumors, which make most population-based series somewhat unreliable [ ]. On the other hand, consultation series or expert center series are likely to over report difficult/unusual cases.

Bone tumors can occur spontaneously; however, a substantial number of them do occur in the context of a hereditary disorder thus implicating a detailed family history in every new case and if suspected for a hereditary context, a proper workup often in close collaboration with clinical geneticists is mandatory [ , ]. This hereditary aspect might explain the higher incidence in some regional populations.

A subgroup of primary bone malignancies occur secondary to benign precursor lesions in the bone such as bone infarction, chronic osteomyelitis, in case of Ollier disease, fibrous dysplasia, or Paget's disease of bone [ ], so the incidence adds up to the occurrence of the primary condition in the population. For instance, there is a well-known regional incidence difference for Paget's disease of bone. Recent attention is drawn to small numbers of cases of bone sarcomas in association with metallic prosthesis and implants; a causal relation, however, is not proven.

Both benign as well as malignant primary tumors of bone are outnumbered by far by metastases to the bone from epithelial cancers or melanoma and hematological disorders like multiple myeloma/plasmacytoma.

Incidence of primary bone tumors

The incidence of bone tumors especially primary bone sarcomas compared to malignant tumors in general is very low. Review of large series revealed that approximately 0.2% of all neoplasms are bone sarcomas [ ]. In Europe about 2 new primary bone sarcomas arise per 100.000 persons a year. Interestingly at childhood there is a steep shift in frequency of occurrence over the age span [ ]. From the first year of life the incidence increases from 3.9 per 100.0000 to a peak of 142.9 per 1000.000 at the age of 15 [ ]. In the archives of the Netherlands Committee of Bone Tumors over 14.000 cases of bone tumors and tumorlike lesions the percentages of the sarcomas in decreasing order of frequency are for malignant bone tumors: osteosarcoma (37%), chondrosarcoma (23.6%), Ewing sarcoma (12.2%), undifferentiated pleomorphic sarcoma of bone (10.9%), non-Hodgkin lymphoma of bone (3.3%), malignancy in giant cell tumor (2.3%), Paget's sarcoma (1%), and adamantinoma (0.8%) [ ].

Fibrosarcoma and malignant fibrous histiocytoma are a diagnosis of exclusion and not frequently encountered anymore nowadays. This is reflected by a change in insights with regard to classification of these tumors, which in practice commonly appear to be poorly differentiated osteosarcoma, or dedifferentiated chondrosarcoma. A terminology of undifferentiated pleomorphic sarcoma of bone is nowadays preferred, acknowledging the fact that true histiocytic differentiation is lacking in these tumors. For benign tumors enchondromas are the most frequent (27.7%) followed by giant cell tumors (21.5%), osteochondroma (14%), osteoid osteoma (10.5%), chondroblastoma (9%), and osteoblastoma (5.7%) [ ]. An age-dependent frequency difference is present, however [ ], as discussed in the following section.

Age

Bone tumors have an age-related presentation. There are two age-specific peaks in frequency in bone sarcomas. The first peak occurs in the second decade of life and consists of osteosarcoma and Ewing sarcoma in case of malignant tumors and osteochondroma in the benign group [ ]. The second peak, slightly increasing from the fourth decade, has its top after the sixth decade and includes chondrosarcoma, undifferentiated pleomorphic sarcoma, chordoma, and osteosarcoma, including Paget's and radiation-induced sarcomas. Chondrosarcomas are somewhat equally distributed over all decades, rarely found in the first 20 years and slightly increasing thereafter. Malignant progression of osteochondroma, as in multiple osteochondroma, is only seen a number of years after closure of the growth plate and can be recognized by restart of growth of the cartilaginous cap of a preexistent osteochondroma [ ].

The majority of benign bone tumors and tumorlike lesion in young patients are seen in the first and second decades of life. In about half, the median age is in the second decade (solitary bone cysts, aneurysmal bone cyst, nonossifying fibroma, fibrous cortical defect, enchondroma, Langerhans cell histiocytosis, osteochondroma, chondroblastoma, osteoblastoma, and osteoid osteoma). The median age incidence of the others is not specific age-related and may be seen in the first decade extending even into the sixth or seventh decade (i.e., juxtacortical chondroma, parosteal osteosarcoma, desmoplastic fibroma). Giant cell tumors occur almost exclusively after closure of the epiphyseal plate.

Gender

The male–female ratio has little diagnostic contribution for most bone tumors, as in general there is no striking difference and both sexes are roughly equally affected. In osteosarcoma the male–female ratio is 1:1. In Ewing sarcoma, Paget's sarcoma, chordoma, and primary osseous non-Hodgkin lymphoma there is a higher prevalence in males (2:1). There is some male predominance seen in some benign lesions like osteochondroma, chondroblastoma, osteoid osteoma, solitary bone cyst, or osteoblastoma. Whether this correlates to a higher incidence of trauma in male, which attracts attention to an underlying, previously asymptomatic tumor is unknown.

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