What is deep soft tissue leiomyosarcoma?

Leiomyosarcoma is a rare form of cancer, characterised by the development of a malignant tumour from smooth muscle cells present in the deep soft tissue, often in the internal organs or vascular areas (places with a rich blood supply).¹ Though it is an extremely rare condition (estimated at 11.5 per million cases per year), it does represent a significant proportion of soft tissue cancers.² Most patients diagnosed with this are over 40 and a higher proportion is found in females as leiomyosarcoma can also be present in the uterus.³

As these tumours develop deep within the body, they can be difficult to diagnose, particularly early on. Contributing to this difficulty is a lack of specific symptoms, meaning that it can easily be misdiagnosed or go untreated for a long time when treatment is urgent.⁴ Treatment is also a challenge as leiomyosarcoma is not very effectively treated by chemotherapy or radiotherapy, so surgical resection (cutting out the tumour or parts of organs) is the most effective (and often only) possible treatment. In addition, the recurrence of this cancer, even after treatment, is common, particularly in the lungs and the liver.¹

Early and accurate diagnosis can improve the treatment of patients and have a positive impact on prognosis and survival. This can prevent the tumour from penetrating deeper structures and allow full resection to be achieved whilst removing as little healthy tissue as possible, leading to a better long-term outcome with an improved survival rate.⁵ Delayed diagnosis may give the tumour more time to spread, making treatment much more challenging, and treatment will often be much less effective, so the planning of complex surgery is much more successful when accurate imaging can be used.

Conventional imaging modalities and their limitations

Ultrasound

Ultrasound is a highly accessible tool, being both cheap and quick. This is often used as an initial assessment if a soft tissue lump is suspected. This can confirm the diagnosis of a tumour and can also identify properties of tumours, including dimensions and whether it is cystic or solid. If a biopsy is necessary, then ultrasound can be further used to direct this process to be more accurate and can be used to monitor changes after treatments or just generally over time.⁶

The most crucial challenge that is encountered when using this modality for diagnosing leiomyosarcoma is that there is a limit to the depth that ultrasound can image, and as leiomyosarcoma is found in the deep tissues, this is a major issue. Furthermore, the quality of soft-tissue contrast is lower than other modalities, and it can be much harder to accurately distinguish properties of tumours, which would provide helpful information for diagnosis and treatment. Large tumours or unusual shapes may also be difficult to distinguish, particularly if they are larger than the field-of-view, limiting the ability to make certain diagnoses.⁶ 

Computed Tomography (CT)

CT provides a 3D image that can accurately show the shape and size of a tumour, as well as the organs that surround it. This modality has a greater ability to distinguish particular identifying characteristics that provide useful information on the type and severity of tumours. There is also a high quality of soft-tissue contrast with this technique. Specific stages can further be identified, and planning using 3D reconstructions is highly useful for effective treatment.⁷

Negative aspects of using this modality include the radiation exposure that patients would be subject to. However, these are relatively low and weighing up the risk of radiation effects with the benefit of accurate imaging in this scenario, CT would be worth it. Another risk involved in this modality is the tendency for CT to overestimate the size of tumours. This is because it is sometimes difficult to distinguish the surrounding tissue from tumours, so they may appear to be larger on a scan than they are in reality. CT scans’ strengths lie in soft tissue imaging and are not as good at developing bone image detail as MRI or other methods, so they can be less effective at diagnosing early tumours in the bone marrow.⁸

Radiography (x-ray)

This method of x-ray is highly useful as a widespread screening tool if leiomyosarcoma is suspected, as it is readily available to a large population and relatively low-cost. By obtaining radiographs at different angles of areas where a tumour is suspected, a tumour can be confirmed. On an x-ray, characteristics such as mineral deposits are identifiable and can strongly indicate the presence of a tumour within soft tissue mass. This can also assess how much adjacent bones have been affected, as tumours can sometimes cause bone remodelling or start to invade the bones.⁸

Whilst this modality can show the effects and chemical traces of this disease, they have very poor contrast for soft tissue and cannot accurately show the size and shape of tumours, with softer tumours often not showing up at all. A further challenge when using x-rays is that they are two-dimensional images, which makes it harder to extract 3D information, making assessment of depth and spatial orientation challenging.⁸

Advanced imaging modalities

Magnetic Resonance Imaging (MRI)

MRI can image soft tissue with high contrast, allowing the precise size and location of tumours to be identified, providing crucial information that can be instrumental in improving treatment. Another benefit of MRI is that it poses absolutely no threat to the patient, as no radiation is involved, so it is risk-free.⁹

This technique usually shows the tumour as a soft tissue mass that is evident in images. Additionally, diffusion-weighted imaging can show information related to tissue cellularity and cell membrane integrity. Further use of techniques such as diffusion-weighted imaging, which can illustrate how aggressive a tumour is, and dynamic contrast-enhancement, which is highly useful in assessing the effect of a tumour on the vascular system.¹⁰

Positron emission tomography - computed tomography

This method uses a combination of PET and CT scanning to provide metabolic information that can be used alongside anatomical imaging to give a clearer picture of what is happening in the body. Areas that uptake a specific molecule associated with tumours common in this disease can be mapped to indicate whether the disease is present and the location of this in the body. However, this method can also be subject to false positives and may miss some types of humours which do not exhibit the same chemical features that this modality can visualise.¹¹

PET-MRI

PET-MRI uses a combination of PET and MRI modalities to illustrate the metabolic pathways as well as specifically image deep soft tissue sarcomas (malignant cancers). This shows the structure and function of the disease within the body, providing more useful information on how to treat the disease with a reduced radiation risk. On the other hand, this MRI technology is much less readily available and time-consuming, so it is rarely used.¹²

Summary

Leiomyosarcoma is a rare deep tissue cancer that can be difficult to diagnose or visualize the extent of due to the depth of the tissues that it affects. Accurate imaging tools can allow diagnosis to be made, the severity of the disease to be understood and facilitate an effective treatment plan to be made and monitored.

The modalities of ultrasound and radiography, which are currently used, are highly useful for screening due to being so readily available and relatively cheap and quick. Ultrasound also has the advantage of being non-ionising, which reduces further harm that may be done to patients from radiation used by X-rays and CT. However, these modalities struggle to accurately distinguish the size and shape of tumours deep within the body, so they may be useful in diagnosis, but further imaging may be necessary to plan and monitor treatment. CT is the most effective method of assessing tumour size accurately and can be instrumental in planning effective treatment.

Further use of advanced imaging modalities, such as PET-CT and PET-MRI, uses a combination of methods in order to obtain information on the metabolism of the disease as well as the physical aspects of the disease to more accurately assess the extent of disease and provide a detailed treatment plan. Overall, these advanced imaging techniques are the most effective modality to combat this disease. However, they are still in the early stages of being used, so they may only be offered in specific circumstances.