Bone cancer is known to be rare, aggressive and associated with abnormal growths (tumours) affecting the bones. However, there are some tumours that are benign or non-malignant (noncancerous). Benign tumours generally do not spread to other parts of the body, known as metastasis, but malignant ones do. 

Osteoblastomas are benign bone-forming lesions that account for 1% of the primary bone tumours and about 1 to 5% of benign bone tumours.¹ This condition predominantly affects the spinal cord and sacrum, the mandible (jaw) and long tubular bones such as the femur or tibia (bones present in the thigh and leg respectively). However, any bone could be affected.^2,3 

Understanding osteoblastoma

Characteristically, osteoblastomas are 2cm or larger⁴ and arise from cells called osteoblasts which play an essential role in forming, growing and healing bones. Osteoblastomas can grow and expand within the bone causing damage to the bone tissues. This results in the replacement of the healthy bone tissue with a less densely mineralized organic tissue called osteoid, which is more prone to fractures. Therefore, although osteoblastomas are benign, they can cause significant bone destruction, disruption of soft tissues and extension of the epidural space (around the spinal cord).

Diagnosis

A combination of clinical, radiological and histopathological examinations are required for an accurate diagnosis.

Osteoblastoma initially presents with symptoms including swelling, decreased range of movements and dull localised pain. 

When the spine is affected, it can cause symptoms such as:

• Back pain
• Scoliosis (curvature of the spine)
• Muscle weakness due to the compression of nerves by the tumour

In addition, a rare variant called toxic osteoblastoma can cause other symptoms including fever, weight loss and anorexia (an eating disorder characterised by restricted food intake).⁵

An X-ray, CT or MRI scan may be required first to identify any changes in the bone structure or detect abnormal growth of tissues in the bones. CT (Computed tomography) scans are able to identify the location, size and borders of the lesion in the bone as well as the relation with the surrounding anatomical structures. 

To diagnose osteoblastoma, the presence of persistent symptoms and a biopsy is required to be taken from the site of the lesion. A biopsy consists of taking a sample from the affected tissue in order to examine and identify the cause at a cellular level, known as histology. 

Since osteoblastomas can become aggressive in some circumstances, surgical excision should be performed early. This helps to speed up the process of diagnosis, prognosis and treatment.

Treatment

The treatment of osteoblastoma includes:

• Surgical removal of the tumour, known as marginal resection

Surgeons would have to outline the margins of the tumour (where the affected tissue ends and the healthy tissue begins) to ensure complete removal of the tumour. 

• Curettage or scraping of the tumour and refilling the site with a bone graft (healthy tissue from other bones or a donor).

• Spinal fusion consists of realigning and fusing the weakened spinal bones which heal into solid bone after removal of the tumour. By fusing the spinal bones together and potentially incorporating pins and rods into the spine, support is provided to the remaining spinal structure after surgery.

In addition, chemotherapy and radiotherapy are used under rare conditions where the tumour cannot be removed safely, for example, if it is located in the spine.

Can osteoblastoma return after being treated?

When a tumour is removed, there is always a risk of the tumour coming back, this is known as recurrence. Osteoblastoma has an excellent prognosis, with only 9.8-15% chance of local recurrence.⁶ Recurrence of the tumour is linked to an inadequate resection of the primary lesion, where the margins are not completely removed. This could be due to the difficulty of safe removal and possible complications.⁷ Chemotherapy is also used in this circumstance if there is a recurrence or if it becomes more aggressive in terms of growth. This demonstrates the necessity to perform a wide local excision or removal of the tumour with wide safety margins to minimise the risk of the tumour growing back.

Can osteoblastoma evolve into osteosarcoma?

Although osteoblastomas are mostly benign, they can still be classified as aggressive tumours depending on how they act. Aggressive osteoblastomas, referred to as osteoblastoma-like-osteosarcoma, are seen to have a higher growth potential, are larger in size, demonstrate increased cellular atypia (abnormal appearance of cells), increased cell division and conduct substantial bone destruction.⁸ In comparison, benign osteoblastomas have a well-defined margin and lesser abnormal appearance. The chances of aggressive osteoblastoma growing back is also higher in comparison and chemotherapy is often used as an additional treatment. Aggressive resection of the tumour is also used. This involves an en-bloc resection where the bone containing the tissue is surgically removed and pins are used to restore the structural integrity.

There have been instances reported where an osteoblastoma has undergone malignant transformation into an osteosarcoma, however, it seems that this is extremely rare and could be due to the incomplete removal of the entire tumour and the affected areas.⁹ 

Osteosarcoma is a primary tumour of the bone, consisting of osteoblasts exhibiting abnormal growth and metastasis (spread to other parts of the body). A primary tumour refers to the site of origin where the tumour is first found in the body, whilst a secondary tumour refers to when the tumour has spread and formed in another part of the body.

As with other cancers, genetic mutation is speculated to transform a benign osteoblastoma tumour into a malignant one. This potentiates the importance of closely monitoring the condition and attending follow-ups with a medical professional when someone is diagnosed with osteoblastoma, especially if it comes back (recurrence) or becomes aggressive.

Summary

Osteoblastoma is a bone tumour which is a treatable condition if diagnosed correctly and early on. So it is essential to follow up with the GP if you have persistent dull pain, do not respond to anti-inflammatory medication or notice a lump in your body. If suspected, the GP will refer you to a specialist for further investigation and confirmation of diagnosis. Treatment will depend on the location and extent of the tumour. The specialist will assist in making an informed decision on the treatment or procedure required. The success rate of complete tumour removal is very high overall and the chances that it will come back again is very low. So, it has a good prognosis and altogether a positive outcome. 

FAQs

Are there any risk factors for developing osteoblastoma?

Definite risk factors are not established yet. Osteoblastoma affects a wide age group (6-75 years) but it is mostly associated with adolescents and young adults. It is more prevalent in people assigned male at birth compared to people assigned female at birth as well.

Can an MRI tell if a tumour is benign?

Whilst an MRI alone cannot determine whether the tumour is benign by itself, it can help to identify the tumour’s likeliness of being malignant. These include the tumour’s characteristics, location, borders and size. Paired with a biopsy, a pathologist can determine if the cells are cancerous or non-cancerous.

Is there another type of benign bone tumour?

Yes, there is. Osteoid osteoma is another benign type of bone tumour. These are quite similar to osteoblastomas, so it is important to distinguish between the two for the correct treatment plan. In terms of symptoms, dull pain is present with both tumours, but the pain worsens at night with osteoid osteoma and can be relieved by anti-inflammatory medication. On the other hand, salicylates such as Aspirin do not relieve pain caused by osteoblastoma. The appearance also differs between the two, as the osteoid osteoma lesions appear to be smaller and limited, whilst osteoblastomas are large and are able to grow/spread to other parts of the body. 

What can delay the diagnosis?

Ignoring symptoms can lead to a delay in the diagnosis of osteoblastoma, due to the numerous other conditions that dull pain is associated with, as it could not raise concerns and may be overlooked.  As the accuracy of the diagnosis relies on a biopsy test and scans, identifying and distinguishing osteoblastoma from osteoid osteoma and aggressive osteoblastoma is also crucial to ensure the right treatment.

Are there less invasive treatments for osteoblastoma?

As treatments for osteoblastoma are quite invasive, a technique called radiofrequency ablation (RFA) can be considered. Guided by a CT scanner, this method utilises a probe with high-frequency alternating currents to create heat on the probe’s tip to destroy the tumour directly. The risks associated with this method include experiencing some pain or burning sensation at the tumour site, and in rare occasions, nerve damage can occur. Infection and bleeding also may occur at the site where the probe is inserted into the body. Although there are risks with this procedure, the success rate is seen to be very high for the first treatment at 94% and 100% after the second treatment.¹⁰ Surgery is still the most commonly used gold standard treatment for osteoblastoma but this technique (RFA) is producing promising results.