Introduction
Primary bone cancer (PBC) is a very uncommon cancer of the bone. It accounts for approximately 0.2 percent of all malignancies worldwide and is idiopathic in the majority of cases. However, there are multiple variants, among which the most common are osteosarcoma, chondrosarcoma, and Ewing sarcoma. Each tumor has different biological behavior, imaging appearance, and demographics. They are typically aggressive and necessitate early detection through imaging and tissue biopsy. Radiation and chemotherapy are frequently combined with surgical excision as the basis of primary bone cancer treatment.
What Are Rare Primary Bone Cancers?
Bone and cartilage cancers are examples of rare bone cancers. Depending on where they reside in the body, they may be given different names. Rare bone cancers that affect children, adolescents, and young adults include:
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Chordoma - Chordoma is a slowly expanding cancer of the spine's tissue. Chordoma can occur at any point along the spine. It is most commonly located near the tailbone (referred to as a sacral tumor) or in the area where the spine joins the skull (referred to as a clival tumor). Chordoma is also known as a notochordal sarcoma.
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Adamantinoma - Adamantinoma is a type of bone cancer that is extremely rare. The majority of the time, it develops in the lower leg. It frequently begins as a bump in the middle of the shinbone (tibia) or calf bone (fibula). Adamantinoma can also develop in the jaw bone (mandible), forearm, wrists, or feet. An adamantinoma lump can be painful, large, and red, and it can impair movement.
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Chondromyxoid Fibroma - Chondromyxoid fibroma (CMF) is a cartilage tumor that grows between the bones. Cartilage is a rubbery material that cushions and shields the ends of the bones rests between the spinal disks, and forms the ear and nose. CMF tumors are noncancerous. While CMF tumor cells can not spread to other parts of the body similar to cancer cells, they can infect surrounding tissues and cause other symptoms.
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Chondrosarcoma - Chondrosarcoma is a type of bone tumor composed of cells that produce an abnormally large amount of cartilage. Cartilage is a flexible tissue that makes up many structures in the body (including the ears and nose). Cartilage also protects the ends of the bones and acts as a cushion.
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Osteosarcoma of the Periosteum - Periosteal osteosarcoma is a rare form of bone cancer. It commonly occurs on the surface of the tibia and femur bones of the legs. It can also occur on the surface of the ulna and humerus bones in the arms.
Around five to ten percent of primary bone cancers are rare primary malignant bone sarcomas (RPMBS), which pose a significant diagnostic difficulty in addition to osteosarcoma, chondrosarcoma, chordoma, and Ewing sarcoma. Spindle cell and round cell sarcomas, as well as hemangiopericytoma-like and vascular tumors, are examples of these malignancies. In patients with primary bone cancers, various histotypes that are often characterized in the soft tissues have also been recorded. These include myxofibrosarcoma, synovial sarcoma, and malignant peripheral nerve sheath tumors of bone.
What Are the Treatment Challenges in Patients With Rare Bone Cancer?
Primary bone cancer management necessitates a multidisciplinary approach involving a specialist bone cancer center, including specialists experienced with offering age-appropriate care for children or adolescents. Several factors influence treatment, including tumor type, stage or grade, and patient preference. Surgical excision is still the primary form of bone cancer treatment. Newly administered and adjuvant forms of chemotherapy are also commonly employed in the treatment, with radiotherapy being used in rare circumstances.
Rare bone cancers present a unique set of challenges due to their rarity. Patients with rare cancers may face discrimination solely because of the disease's rarity. Pediatric malignancies have also been affected by a variety of obstacles associated with uncommon diseases, as they frequently necessitate specialized methods due to their age-related biological, clinical, and organizational aspects. The following are some of the common challenges seen in patients with rare bone cancers.
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Incomplete or inaccurate diagnosis.
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Inaccessibility to appropriate treatments and expertise.
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Lack of commercial viability in developing novel medicines.
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Difficulties in carrying out well-powered clinical trials.
What Are the Latest Treatment Methods for Rare Primary Bone Tumors?
Traditional treatment using certain combinations of chemotherapy, surgery, and radiation has reached its efficacy limit, with significant room for improvement in patient outcomes. Additionally, genomic analysis of these cancers revealed a scarcity of treatable molecular targets. Recent advancements in cancer immunotherapy constitute a bright side in the treatment of primary bone cancer against this backdrop. Cancer immunotherapy techniques include naturally existing anti-tumor T cell stimulation and adoptive transfer of tumor-specific cytotoxic T cells. Chimeric antigen receptor T cells (CAR-T cells) are part of the latter method and are an amazing use of both T cell biology knowledge and genetic engineering developments.
Despite the extraordinary success of CAR-T cell therapy in numerous cancers of the blood, its application in solid bone tumors remains difficult. The selection of appropriate antigens to target and the immunosuppressive tumor microenvironment (TME) are significant challenges. An ideal chimeric antigen receptor target should be substantially expressed on the surface of tumor cells while being absent in normal tissue. As only a tiny proportion of proteins expressed by cancer cells are found on the cell surface, the selection of chimeric antigen receptor targets in bone cancer is severely limited. Indeed, the transgenic T cell receptor method may be more appropriate because it can potentially target any antigen presented by a major histocompatibility complex (cell surface or internal). However, solutions for circumventing this limitation of CAR-T cell treatment are constantly being researched.
Conclusion
Primary bone cancer is a rare diagnosis. The process of diagnosing primary rare bone cancer begins with a review of the patient's medical history and physical examination. If a diagnosis is made, all patients must be referred to a specialized facility for appropriate treatment. Due to its rare incidence, primary bone cancers lack a definite treatment protocol.
