What is a lipoma and how is it diagnosed?
A lipoma is a benign (not cancerous) tumor composed of mature fat cells, originating from the mesenchymal tissue. Mesenchymal tissue is a type of connective tissue that is present under the skin. Lipoma is the most common type of growth in soft tissue, accounting for almost 50% of soft tissue tumours. They occur in up to 2% of the world's population [1]. Lipomas can develop anywhere on the body, though they occur more frequently in the areas rich in adipose (fat) tissue, including the neck, shoulders, thighs and arms [2].
Lipomas present as a slow-growing, painless mass which is mobile (can be moved around through the skin) and has a soft, dough-like consistency [3]. Consequently, the diagnosis of lipoma relies heavily on physical examination by the doctor - the diagnosis can be made on determining the characteristic feel of the lipoma by palpation (touching and feeling the mass) [2, 4].
Imaging, such as ultrasound, may be used to confirm the diagnosis. In the case of suspicion for liposarcoma, a very aggressive cancerous tumour, additional imaging such as a CT scan or magnetic resonance imaging can be performed [5, 4]. In some cases, the doctor may opt for a biopsy - a procedure where a small sample of the tumour is taken with a needle under local anaesthesia [2]. This is followed by a histopathological examination, where a pathologist examines the tissue under a microscope, and uses stains to visualise certain proteins or other molecules.
What is the treatment for lipoma?
As lipomas are not cancerous and grow slowly if at all, treatment is mostly done for cosmetic purposes. In some rare cases with lipomas restricting movement or causing discomfort (such as those located around the joints), removing the lipoma is the primary treatment option. Regardless of the therapeutical goal, lipomas are primarily treated by surgical removal. This is a very simple procedure done in-office under local anaesthesia. A small incision is made in the skin, and the lipoma is removed, sometimes with a small margin of healthy tissue [6]. More treatment options are available, including liposuction, which may be helpful to reduce the tumour size, but sometimes fails to completely remove the lipoma [2, 7]. Various injectable treatments, such as steroid injections [2] or an Aqualyx injection can dissolve the lipoma, thus mitigating the need for surgery. The Aqualyx injection has very good outcomes, achieving a complete removal in 70.59% of cases [8]. Various laser treatments are also avialable, also with excellent outcomes [9, 6].
As the therapeutical options for lipoma are very good, the prognosis for a lipoma is excellent. After treatment, recurrence is not common - for example in a study where patients were treated either by liposuction or surgery, none reported the lipoma coming back [10]. It is, however, important to visit the dermatologist regularly to examine your overall skin health, and discuss potential lipomas early. If you'd like to know more about lipomas and similar masses, we wrote another blog on the differences and similarities of lipomas versus sarcomas, you can read it right here on Medisearch blog.
What is a Liposarcoma?
Liposarcoma is a rare, but aggressive type of cancer that arises from adipose tissue. Liposarcomas are one of the over 70 subtypes of sarcoma - a group of cancers arising from various types of connective tissue [11, 12]. They are most commonly found in the limbs and the retroperitoneum - the space in the abdomen behind the intestines [10, 13].
Diagnosis of liposarcoma
Early diagnosis of liposarcoma (and, in fact, any cancer in general), is essential to improve patient outcomes. Liposarcomas can resemble lipomas in the initial presentation - they also present as soft masses palpable through the skin. It is therefore essential to visit a doctor if you discover such a mass (though it is important to not panic, as liposarcomas are very rare).
Additionally, liposarcomas can present with variety of signs and symptoms some of which are very non-specific, including pain in the area of the tumour, abdominal pain, feeling of fullness without eating, weight loss, fatigue, limited mobility of a joint or swelling, or numbness or tingling when the tumour is next to nerves.
Diagnosis of liposarcoma involves a physical examination, followed by diagnostic imaging such as an ultrasound, computed tomography (CT) or magnetic resonance imaging (MRI). These tests are essential in establishing the size of the tumour, as well as elucidate the surrounding anatomy [14].
How is Liposarcoma diagnosed?
Liposarcoma is diagnosed through a combination of imaging tests and tissue examination:
- Imaging tests: CT scans and MRIs can help determine the size, location, and fat content of the tumor. Higher fat content suggests a benign lipoma, while less fat is more consistent with liposarcoma [19]. In one study, 60% of liposarcomas appeared as ill-defined masses with CT numbers ranging from -40 to +28 HU [20].
- Biopsy: A definitive diagnosis requires a tissue biopsy. This may involve removing the entire tumor or taking a sample using a needle guided by imaging [21], [19].
- Pathology: The tissue is examined under a microscope by a pathologist. Immunohistochemistry for markers like S-100, p16, and CDK4 can help confirm the diagnosis. In one study, 79%, 79%, and 71% of liposarcomas were positive for these markers, respectively [22].
- Genetic testing: Fluorescence in situ hybridization (FISH) can detect amplification of the MDM2 and CDK4 genes, which is characteristic of liposarcoma [23].
This is important for the planning of surgery when the tumour is resected. A biopsy (a procedure where a small sample of the tumour is taken with a needle under local anaesthesia) is also needed to confirm the diagnosis. The sample is then investigated under the microscope and stained for presence of certain molecules which can reveal the subtype of the tumour and help guide drug selection during therapy.
Molecular (genetic) investigations are also important in the diagnosis of liposarcoma. Fluorescence in-situ hybridization (FISH) is used to identify specific genetic markers, such as translocations (occurrence where pieces of chromosomes (units to which DNA is organised) swap places and jump to different chromosomes), or presence of MDM2 protein or CDK4 amplification [13].
Treatment of Liposarcoma
The primary treatment for liposarcoma is surgery to remove the tumor with wide margins (a region of healthy tissue around the tumour is also removed to ensure that all potentially cancerous cells are taken out) [12].
Surgery is often followed by radiotherapy to the tumour site to kill any remaining cancer cells and reduce the risk of recurrence [15]. The exact surgical approach depends on the tumour size and location - unfortunately not all liposarcomas can be taken whole due to complicated anatomy around the tumour (such as joints, tendons and nerves which should not be damaged by the surgery).
Cytotoxic chemotherapy is also used in management of liposarcoma, with doxorubicin and ifosfamide being the first-line treatments. In the second line, gemcitabine, docetaxel, trabectedin, and eribulin are used.
Unfortunately, liposarcomas are not typically sensitive to traditional chemotherapy and radiotherapy [11]. Therefore, there is an urgent need to implement novel targeted therapeutics or immunotherapeutics. Targeted therapies aim to distrupt a molecule essential for the survival of the given tumour.
In liposarcoma, these include CDK4 and MDM2 - inhibitors of both are used in the clinic. Additionally, immune checkpoint modulators, nuclear export inhibitors, multi-kinase inhibitors, and peroxisome proliferator-activated receptor gamma agonists can be administered [16]. Some of these are approved, whereas others are accessible to patients via clinical trials - Patients with liposarcomas are also encouraged to participate in clinical trials, especially when the standard therapeutical options are exhausted without sufficient results. Participation in clinical trials helps the scientific community evaluate novel treatment options and strategies, and trials generate invaluable data that help guide new policy, while providing potential benefit to the patient.
Prognosis of Liposarcoma
The prognosis of liposarcoma depends on the tumour type and stage. However, the overall survival rate for liposarcoma patients is around 48.1% at a median follow-up of 8.6 years [17].
While well-differentiated liposarcomas generally have a better prognosis, badly differentiated tumours and pleiomorphic liposarcomas (tumour with different forms and types of tissue in a single structure) have a worse prognosis and are more challenging to treat [14].
Differentiation of a tumour is a measure of how much the cells within lose their natural function - high differentiation means that the cells assume physiological subtypes (such as muscle cells, fat cells, ...), whereas low differentiation means that the cells completely lost their physiological phenotype.
Summary: What is the difference between lipoma and liposarcoma?
Lipoma and liposarcoma are two different conditions that both form in fatty tissue and cause lumps, but they have significant differences. The most crucial distinction is that lipoma is noncancerous (benign), while liposarcoma is cancerous (malignant) [18].
Lipomas are benign tumors that form just under the skin, and they tend to feel soft or rubbery and move when you push with your fingers. They're normally painless and not likely to cause other symptoms. Importantly, they do not spread [18].
On the other hand, liposarcomas form deeper within the body, usually in the abdomen or thighs. If untreated, they can spread throughout the body [12, 18]. Early detection and action is important, therefore, an early visit to a medical professional is essential if you notice any lumps on or under the skin.