Osteoblastoma vs Osteosarcoma

Overview

Have you got a passion for bones and their pathologies? Do you want to learn more about bone tumours and their types? In this article, we will be covering two interesting diseases: osteoblastoma and osteosarcoma. So, what are they? Both are tumours of the bone however, one is benign while the other is malignant and they usually occur in young adults/teens.^{1, 2} To better understand the differences between the two, this article will provide a comparison between the two illnesses. So let us dive in.

Osteoblastoma

Definition and characteristics

As mentioned in the introduction, osteoblastoma is a type of bone tumour.¹ It is defined by marked new bone production/formation with vascularised lesions.³ The production seen in osteoblastoma tends to be in the form of trabecular bone that lacks organisation, a low abundance of nerve fibres, and prostaglandins.³ Malignant transformation and metastatic diseases have been reported and associated with osteoblastoma.³

Epidemiology

Osteoblastoma is the most common benign primary bone tumour and predominantly affects children aged between 10 to 15 years and young adults (20 years old) and is more common in people assigned male at birth than people assigned female at birth.^{1, 3} It is also known for its osteoblastic (bone formation) nature and local aggression, which is slightly more common in older patients (33 years old).¹ Throughout different studies, it was concluded that osteoblastoma makes up 1 to 5% of all benign tumours and 1% of all bone-related tumours.^{1, 4}  

It is commonly present in the spine and sacrum (around 28-55% of cases) involving the posterior elements of the spine however, it can also be present in other areas such as the femurs (12%), the jaw (11%), the tibia (10%), and the feet and ankles (9%).^{3, 4}

Signs and symptoms

Signs and symptoms in osteoblastoma can sometimes be hard to see; at times, osteoblastoma presents itself as an asymptomatic, or slow-growing tumour and is picked up when performing tests for other causes and reasons such as aneurysmal bone cyst.^{4, 5} However, in the case of a symptomatic osteoblastoma, the common symptoms include swelling and localised pain that is not responsive to pain relievers or NSAIDs, along with the presence of fever and weight loss.⁴

When referring to osteoblastoma on a histological scale, it is a benign bone-forming tumour which is similar to osteoid osteoma (which is a tumour that has no potential to be malignant). In fact, it used to be referred to as a giant osteoid osteoma due to the similarities between the two.^{1, 3} Although both of these cases are derived from the same osteoblastic lesional process, osteoblastoma is typically more aggressive clinically and radiologically.¹

In 1984, Dorfman and Weiss introduced a new term called ‘aggressive osteoblastoma’ which is a borderline osteoblastic tumour entity; it was associated with a high recurrence rate and potential for malignant development and transformation.¹ Even though osteoblastomas are benign tumours, they can cause significant bone destruction, soft tissue infiltration and epidural extension.¹ 

If left untreated, the distal aggressiveness of the tumour can lead to malignant transformation and the destruction of the spine, with a high risk of neurological deficits in severe cases.¹

Causes

Currently, it is not known what causes osteoblastoma and what the risk factors are for this case.^{3, 5}

Testing and diagnosis

Testing for  osteoblastoma can be done in various ways:⁵

• X-rays: To see the images of the bones
• Magnetic resonance imaging (MRI): Incorporates the use of large magnets, radio frequencies, and a computer to give detailed images of organs, soft tissues, muscles, ligaments, and other structures inside the body.
• Computed tomography (CT) scan: This involves the use of X-rays and computer technology to produce cross-sectional images, known as "slices", of the body.
• EOS imaging: An imaging technology that creates 3-D models from 2 planar images. Unlike a CT scan, EOS images are taken while the patient is in an upright/standing position, which enables improved diagnosis due to weight-bearing positioning.
• Needle biopsy: This involves the use of a small needle that is inserted through the skin and into the lesion to withdraw a small sample of the aberrant tissue. The tissue is later analysed to confirm any findings.

Osteosarcoma

Definition and characteristics

Osteosarcoma is the most common type of bone cancer that occurs in children and adolescents and 3^rd most common in adults.^{2, 6} It is derived from bone-forming mesenchymal cells.² It can occur in 2 forms: the first one has no underlying bone pathology and the second with underlying pathology that had malignant degeneration or conversion occur.⁷ Osteosarcoma represents itself as highly heterogeneous and this leads to several subtypes being differentiated based on the degree of tumour differentiation, location in the bones and histological variations.⁷

Epidemiology

Osteosarcoma has a bimodal age distribution; the initial peak is in patients aged 10-14 which is linked to a pubertal growth spurt, while the next observable peak is in adults (>65 years old) where the malignancy is secondary to other diseases such as malignant degeneration of Paget disease, bone infarction and others.⁷

There are other factors such as race and sex that play a role in osteosarcoma; Black people are the ethnic group that predominantly face osteosarcoma, followed closely by Hispanics and white people respectively.⁷ Additionally, males assigned at birth have higher incidences than females assigned at birth.⁷

Osteosarcoma commonly occurs close to the metaphysis of the long bones of the appendicular skeleton.⁷ The most common locations are:⁷

• Femur: 42%, with 75% of tumours in the distal portion of the bone
• Tibia: 19%, with 80% of tumours in the proximal portion of the bone
• Humerus:10%, with 90% of tumours in the proximal portion of the bone
• Other potential sites include the skull/jaw (8%) and the pelvis (8%)

As mentioned before, osteosarcoma can be categorised into primary and secondary forms:⁷

• Primary tumours: usually occur in the metaphysis of long bones (mostly in the knees); around 60% occur in this area. These tumours occur mostly in children and adolescents.
• Secondary tumours: have a much wider distribution which is linked to the varied nature of their underlying predisposing condition. It is more common in flat bones, particularly the pelvis, and is almost always in the adult population. 

Signs and symptoms

Symptoms associated with osteosarcoma can be present for a long time (weeks/months) before the patient goes for a diagnosis.⁷ The most common symptoms include bone pain, especially during activity.⁷ Other symptoms include:^{7, 8}

• Swelling around the affected site
• Limping
• Decreased movement of the affected limb
• Fever and night sweats
• Local or regional lymphadenopathy (uncommon)
• Respiratory findings with metastatic forms (rare)

Causes

The cause of osteosarcoma remains unclear however, there have been studies regarding the roles of genetics, epidemiology and environment.⁷ Some of these genetic alterations in cases of primary osteosarcoma include:^7,8 

• Hereditary Retinoblastoma
• Li-Fraumeni Syndrome
• Rothmund-Thomson Syndrome
• Bloom Syndrome
• Werner Syndrome

Testing and diagnosis

In addition to a complete medical history and physical examination, it would be required to check for osteosarcoma using diagnostic tests such as:⁸

• X-rays: Used to produce images of internal tissues, bones, and organs on film.
• Bone scans: This is a nuclear imaging technique used to evaluate any degenerative and/or arthritic changes in the joints. This is done to scan for any bone diseases and tumours and to determine the cause of bone pain or inflammation.
• Magnetic resonance imaging (MRI): Used to produce detailed images of organs and structures inside the body. This method is performed to better define a mass captured on X-ray and to look for any nearby spread of tumours.
• Computed tomography scan (CT or CAT scan): An imaging test that uses X-rays and a computer to make detailed images of the body. A CAT scan shows details of the bones, muscles, fat, and organs.
• Positron emission tomography (PET) scan: A radioactive-labelled glucose (sugar) is injected into the bloodstream and scanned for use; as tumours use more glucose than normal tissues they can then be tracked down. PET scans can be used to find small tumours that have spread or to check if treatment for a known tumour is working.
• Complete blood count (CBC): Includes a measurement of the size, number, and maturity of different blood cell types.
• Other blood tests: Such as blood chemistry
• Biopsy of the tumour: Tissue samples are removed (using a needle or during surgery) from the body for examination under a microscope to determine if cancer or other abnormal cells are present.

Treatment methods and therapy

Treatment for osteoblastoma and osteosarcoma may include:^{5, 8}

• Surgery: Examples include biopsy, bone/skin grafts, resections, limb salvage procedures, reconstructions, or even amputation.
• Chemotherapy
• Radiotherapy
• Rehabilitation: This can be practised as physical therapy, occupational therapy, and psychosocial adapting
• Prosthesis fitting and training
• Antibiotics to prevent/avoid and treat infections
• Supportive care
• Continuous follow-up 

It is important to treat osteoblastoma and osteosarcoma to avoid future complications and have a better prognosis and survival rates. Please refer to your healthcare provider for further details or advice.

Summary

Osteoblastoma and osteosarcoma are rare bone-forming tumours that might not be easily detected from general symptoms. While osteoblastoma is usually benign, osteosarcoma is a more aggressive type of tumour that is malignant. Osteoblastoma tends to affect the lower vertebrae of the spine or long bones of the lower extremities, while osteosarcoma occurs in the long bone around the knee. Both require attention and medical care to manage the severity of the illness and help provide the patient with the best outcome possible.