The relative frequency of more common benign bone tumors has been discerned from prior publications and extrapolation from the primary contributor’s case registry of consecutive surgical cases treated between 1991 through 2004. It should be noted that although Dr. Ward’s personal tumor registry has been updated since 2004, in 2005 additional providers joined his group and began to share care for this cohort of patients. With the resulting tempering in his experience, accurate incidence estimates could no longer be extrapolated from his personal tumor database. Table 9A.7.1 reflects the collected experience reported in the Mayo Clinic publication of 1986, the University of Florida publication from 1983, the J. Mirra experience reported in 1989, and the case series reflecting the practice of Dr. Ward, a full-time solo orthopaedic oncologist in practice from 1991 to 2004, at Wake Forest University Health Sciences in Winston-Salem, NC.

The experience of Dr. Ward during the stated time-period is believed to reflect roughly the general prevalence of bone and soft tissue tumors, since he treated a wide variety of benign and malignant bone tumors in a broad referral practice. All cases in his registry reflected his personally treated patients, ie, none were “consult cases” in which only radiographs or pathology slides were reviewed for outside consulting physicians, such as the Mayo and Mirra series included in their registries. The earlier data sets were accumulated during time periods prior to the full development of the subspecialty of orthopaedic oncology; thus, only the more unusual cases of bone tumors were referred to major medical centers, making estimates of their incidence less reliable. It is believed that, with the exception of bone cysts, general orthopaedic surgeons or other musculoskeletal specialists in North Carolina treated few bone tumors over the period the data was collected, as most were referred to orthopaedic oncologists. Practical experience has confirmed that osteosarcoma is the least likely sarcoma to be treated by anyone other than an orthopaedic oncologist. Dr. Ward and a small group of orthopaedic oncologists treated nearly all patients with an osteosarcoma in North Carolina for the past 22+ years.

As such, comparing the cases of benign bone tumors relative to the cases of osteosarcoma treated by Dr. Ward provides a relative index useful in generating a broad estimate of the prevalence of these benign tumors. By comparing this estimate with the national estimate for the annual occurrence of osteosarcoma, the most commonly encountered primary sarcoma of bone, a rough estimate of the incidence and prevalence of these benign bone tumor diseases was calculated. Because the records only included patients treated surgically, incidence and prevalence estimates also include only patients with these disease states that generally require surgical intervention. This selection process likely excludes small benign tumors, thereby artificially lowering the frequency estimates. (Reference Table 8A.7.1 PDF [1] CSV [2])

Osteochondroma
The most commonly encountered benign tumor of bone is osteochondroma, which typically arises near the long ends of bones. Osteochondromas are often painful because of formation of bursae (small fluid-filled sac) overlying the lesion, tenting and irritation of overlying soft tissues, interference with neurovascular function due to tenting of such structures over the osteochondroma surface, and the potential for deformity in the involved and/or adjacent bones. Long-term complications are uncommon except for rare cases of dedifferentiation into a chondrosarcoma. There is no estimate of the number of patients seen with nonoperatively managed osteochondromas due to lack of records. An annual prevalence of >1,500 surgical cases is based on records kept by Dr. Ward; this is believed to be underestimated. Not included in this estimate are cases treated by general orthopaedic surgeons and pediatric orthopaedic surgeons, who, in addition to orthopaedic oncologists, provide surgical treatment of osteochondromas.

Unicameral Bone Cysts
Unicarmeral bone cysts are the second most commonly encountered benign bone lesions, with an estimated annual prevalence of more than 1,250 surgical cases. The etiology of these fluid-filled bone cysts, usually found in the growing ends of children’s long bones such as the proximal humerus or femur, is unclear. Because they never metastasize and are usually quite characteristic on radiographs, many of these are treated by other orthopaedic surgeons, especially pediatric orthopaedic surgeons. The true incidence, therefore, is probably significantly higher than that estimated by extrapolation from Dr. Ward’s practice experience. These cystic lesions cause weakening of the bone and the patients may require multiple surgeries to rebuild the bone with bone grafts, injections, and other techniques. They occur in children, and typically recur multiple times until skeletal maturity is achieved.

Giant Cell Tumor of Bone
Giant cell tumor of bone, with an estimated annual prevalence of more than 750 cases, is the third most commonly encountered benign bone neoplasm, and accounts for significant disability and dysfunction. This typically occurs near the end of the long bones, most commonly the lower femur or upper tibia, and causes destruction of the bone. The tumor may extend through the cortex of the bone into the soft tissues and, if large enough prior to treatment, can be associated with pathologic fracture of the involved bone. Smaller tumors can be treated with bone resection and reconstruction with bone grafts or cement filler. Cases that are more complicated require sophisticated reconstruction with massive joint replacements and/or massive allografts, and can cause severe long-term disability. On rare occasions, giant cell tumors metastasize to the lungs. In such cases, they typically respond poorly to chemotherapy and may cause death. These tumors are rarely treated by general orthopaedic surgeons. Although currently not considered the standard of care, many patients’ tumors have had excellent responses to denosumab treatment, a monoclonal antibody directed against RANK ligand, the activator of osteoclasts (which are giant cells). This is very similar to the mechanism of action of bisphosphonates. Initial studies with denosumab have shown a very favorable response in the majority of tumors so treated, but presently, even with denosumab pretreatment, surgical resection appears to be ultimately required. With enhanced understanding of the underlying pathogenic mechanisms, non-surgical management may become possible in the near future.

Enchondroma
A fourth commonly encountered tumor that may require surgery is enchondroma, estimated at more than 725 annual surgical cases. Bones typically form as cartilage during the embryo stage of human development, and this cartilage model ultimately converts into bone structure. The cartilage-based growth plates add length to the bones from bone growth. Enchondromas are tumors derived from remnants of these cartilaginous tissues that abnormally remain in the skeleton as remnants or nodules from the normal pattern of maturation and development. If these achieve sufficient size, they can cause cortical bone erosion and pain or fracture, and may present diagnostic challenges requiring biopsy. They often require treatment by curettage and bone grafting. These lesions can dedifferentiate into malignant cartilage tumors called chondrosarcomas. Many small enchondromas are seen incidentally, cause no symptoms, and are treated with simple observation; thus, total incidence of enchondromas is much higher than shown in the surgical data. In addition, the burden of enchondromas requiring surgical treatment is very conservatively estimated, as many are treated by general orthopaedic surgeons.

Other Benign Bone Tumors
Multiple other benign tumors are commonly encountered.

• Aneurysmal bone cysts (ABCs) are aggressive cystic lesions similar to unicameral bone cysts. However, ABCs are more destructive, expanding and weakening the bone and causing greater bone destruction. They tend to fill with blood and tissue, not simple fluid. Usually, ABCs respond favorably to curettage and bone grafting, but recur in at least 20% of cases. Some ABCs arise secondarily in other bone lesions and conditions such as fibrous dysplasia.
• Metaphyseal fibrous defects are focal defects in normal bone that are filled with soft tissue. These occur in 2% to 3% of normal children. Most resolve without ever causing symptoms, and may never be detected unless the child receives an X-ray or MRI scan for another problem. Large ones may require surgery, such as bone grafting to prevent fracture and/or surgery to treat completed fractures that have already occurred.
• Osteoid osteoma is a small tumor typically occurring in children that is associated with severe, unrelenting night pain. It usually requires resection or radio frequency ablation and occasionally may require bone grafting. When located in the spine, it can cause a painful scoliosis. Recently, successful treatment with radio frequency ablation under radiographic guidance has become the treatment of choice for accessible lesions.
• Chondroblastoma is an unusual neoplasm that occurs in the ends of growing bones in teenagers and young adults. This requires resection of the lesion and bone grafting. If untreated, it can cause collapse and degenerative arthritis in the associated joint and, on rare occasion, can metastasize to the lung. Chondroblastomas usually are referred to orthopaedic oncologists.
• Numerous other less common benign bone tumors often are treated similarly to giant cell tumors, ABCs, or chondroblastomas with curettage, resection, and bone grafting. Most cause some degree of disability and dysfunction of the involved extremity.

As with the benign bone tumors, there is no national registry of benign soft tissue tumors. By comparing Dr. Ward’s 13 years of practice history from 1991 to 2004, and computing an incidence index relative to that of osteosarcoma, some estimate of the prevalence of surgically treated lesions may be obtained. From this index estimate, a baseline estimate of the national incidence can be calculated. However, benign soft tissue tumors are the most likely category of tumors to be treated by other surgeons, such as general orthopaedic surgeons and general surgeons; therefore, this national estimate is extremely conservative. The prevalence and burden in the United States from benign soft tissue tumors is significantly higher than estimated herein. (Reference Table 8A.7.2 PDF [3] CSV [4])

Detection of the majority of benign soft tissue tumors is from local growth, and may require resection. Benign lesions rarely cause death, and it is rare that an amputation is necessary. However, depending on the site of involvement and size of the lesion, significant disability of the involved extremity and/or joint can occur. The true cost of these otherwise benign neoplasms can be high in terms of healthcare costs, lost work time, morbidity, emotional cost, and disability expenses.    

Tumors of Fat Tissue

Lipomas: Benign tumors of fat tissue
Lipomas are the most common benign soft tissue tumor. Most are found under the skin, but they can develop anywhere in the body. Many lipomas are present for years and inactive, but those that are growing lesions and are probably the most commonly resected soft tissue benign tumor. Resection of growing lesions is usually performed in local community settings by multiple surgical specialists and even by primary care practitioners. Only patients with larger and more concerning lesions are typically referred to surgeons with a focus in surgical oncology. Not infrequently, a slow-growing sarcoma is mistakenly diagnosed as a lipoma, leading to a delay in the diagnosis of soft tissue sarcoma. This misdiagnosis can lead to suboptimal resection of the unappreciated sarcoma by the unsuspecting community surgeon.

Lipoblastomas
Lipoblastomas are benign fat tumors that occur in infants and young children.

Hibernomas
Hibernomas are benign fat tissue tumors that behave similarly to lipomas. They are so named because of their brownish coloration that resembles the appearance of the fatty tissue of bears, hence the name hibernomas. They are much less common than lipomas.

Tumors of Muscle Tissue

Smooth muscle benign tumors
Smooth muscle, found in internal organs such as stomach, intestines, blood vessels, or uterus, involuntarily contracts. Leiomyomas are benign tumors of smooth, or involuntary, muscle. Leiomyomas can arise almost anywhere in the body in either men or women because they start in tissues as widespread, for example, as blood vessels or intestine. The most common of these is the fibroid tumor that often develops in the uterus. It is really a leiomyoma (smooth muscle tumor) of the uterus.

Skeletal muscle benign tumors
Skeletal muscle is the muscle that allows movement of arms and legs and other body parts. These are voluntary muscles. Rhabdomyomas are benign tumors of skeletal muscle and are very rare.

Benign Tumors of Peripheral Nerve Tissue (Benign Peripheral Nerve Sheath Tumors)

Neurofibromas, schwannomas (neurilemmomas), and neuromas are benign tumors of nerves. These tumors can occur almost anywhere in the body. An inherited condition called neurofibromatosis, or von Recklinghausen disease, causes people to develop many neurofibromas throughout their body. Some of these may dedifferentiate and become malignant. These dedifferentiated malignant tumors usually form from large neurofibromas in the upper arms, neck, pelvis, or thigh. Patients with the dedifferentiated neural sarcomas have a very poor prognosis since the vast majority of patients ultimately succumb to the cancer.

Tumors of Joint Tissue

Joints are surrounded by tough tissue called synovium, which produces the fluid that lubricates the joint surfaces so they move smoothly. Joint tissue tumors typically arise from the synovium.

Pigmented villonodular synovitis (PVNS) is a benign tumor of joint tissue. It is most common in its nodular form in the hands, and is more common in women than in men. The nodular form rarely recurs following adequate and complete excision. PVNS also occurs in a diffuse form that typically will involve the entire joint lining and has a high recurrence rate after attempted resections. PVNS in its diffuse form is most commonly encountered in the knee joint, where it often causes recurrent bloody effusions (swollen knees filled with bloody fluid).

Tumors of Blood Vessels and Lymph Vessels

Hemangiomas are benign tumors of blood vessels. They are rather common, are often present at birth, and can affect the skin or internal organs. They sometimes disappear without treatment, but when located in muscles and other deep tissues, can be quite problematic and require surgical treatment.

Glomus tumors are benign perivascular (surrounding blood vessels) tumors. They usually are found under the skin and often under fingernails. They are usually small (<1 cm), but are exquisitely tender and painful. They may make the overlying skin sensitive to even light touch from clothing.

Hemangiopericytoma is a tumor of perivascular tissue. It most often develops in the legs, pelvis, and retroperitoneum (the back of the abdominal cavity) and is most common in adults. These can be either benign or malignant. They rarely spread to distant sites, but tend to recur locally following surgical resection unless very widely excised. They may be multifocal.

Lymphangiomas are benign lymph vessel tumors that are usually present at birth. Lymph is a type of fluid that circulates in every tissue of the body. Lymph fluid is collected and routed back into the venous system by the lymphatic system, and contains waste products from tissues and immune system cells. Lymphangiosarcomas are the malignant lymph vessel equivalents of angiosarcomas.

Tumors of Fibrous Tissue

Fibrous tissue forms tendons and ligaments and covers bones as well as other organs in the body.

Fibromas, elastofibromas, extra-abdominal fibromatosis, and fibrous histiocytomas are all benign soft tissue tumors. Fibromatosis is the most problematic of these tumors. They frequently recur following resection, and may require additional treatment with repeat surgery, radiation therapy, chemotherapy, or other therapies. Although these tumors do not metastasize, they can be challenging. Fibromatoses (desmoid tumors) were discussed at length under the malignant soft tissue section above where they are often grouped due to their aggressive nature.

Tumors of Uncertain Tissue Type

Through microscopic examination and other laboratory tests, doctors can usually find similarities between most soft tissue tumors and certain types of normal soft tissues. This is how soft tissue tumors are classified. However, some soft tissue tumors have not been linked to a specific type of normal soft tissue.

Myxoma is a benign tumor that usually is located in muscles but does not develop from muscle cells. The cells of a myxoma produce mucus-like material, a distinguishing feature of this tumor. They are usually found in adults, and rarely recur after treatment. Myxoma must be differentiated from myxofibrosarcoma, a malignant neoplasm that can appear very similar under the microscope as well as in gross appearance. The challenge for the treating physician is to avoid overtreating myxomas and undertreating myxofibrosarcomas, in terms of the extent of normal tissue margin around the tumor to be resected with the tumor to minimize the risk of recurrence.

Granular cell tumors are usually benign tumors of adults that often occur in the tongue, but can be found almost anywhere in the body. They are frequently multifocal.

Tumor-like Conditions of Soft Tissue

Some conditions of soft tissues are caused by inflammation or injury that forms a mass similar to a soft tissue tumor. Unlike a true tumor, they do not come from a single abnormal cell; they have limited capacity to grow or spread to nearby tissues, and never spread through the bloodstream or lymph system. Examples include nodular fasciitis and myositis ossificans, which involve tissues under the skin and muscle tissues, respectively.1

There can also be deposition tumors. The most commonly encountered ones are tophi, often seen in cases of poorly controlled gout. These tumors can achieve massive size, may be mistaken for true tumors, and erode through the skin, causing skin breakdown and infection that may require surgical treatment and antibiotics. Calcium deposits are often seen in renal failure and in poorly managed dialysis patients. They may be painful and may require difficult resection of deposits infiltrated into normal tissue. When not associated with diseases of abnormal calcium metabolism, such as renal failure and dialysis, the disease is termed tumoral calcinosis. It behaves essentially the same as the calcium deposition mentioned in association with renal disease. Amyloid deposition can rarely cause a soft tissue (or bony) mass. These are most often seen in poorly controlled dialysis patients. Rheumatoid nodules are soft tissue deposits of antibody-laden, inflammatory soft tissue masses that can be quite painful and may require resection for symptomatic relief. Adequate treatment of the underlying rheumatoid arthritis with current disease-modifying medications usually prevents the occurrence of such lesions. 

• 1. National Cancer Society (NCS): Sarcoma: Adult Soft Tissue Cancer? Available at: http://www.cancer.org/cancer/sarcoma-adultsofttissuecancer/detailed guide/index [5]. Accessed March 19, 2015. Editorial revisions provided by William G. Ward, MD.