The introduction of targeted therapy has transformed cancer treatment over the past decade. It is now a component of many cancer management plans; however, each drug has its side effects that may affect the quality of life. This topic will review these side effects and how to address them.  

Overview of targeted therapy 

Your cancer treatment team may have suggested targeted therapy at some point, and you might be wondering about its nature and potential side effects. It was first approved as an anticancer treatment in the late 90s, and since then, it has undergone many advancements including the development of more cancer-specific drugs with more diverse applications such as breast, lung, skin and colonic cancer.​¹​  

In targeted therapy, the drug is designed to attack specific components of cancer cells like some proteins or genes which are either unique to or more prominent in this kind of cells compared to ones, it acts to stop its growth and function. You have to have this specific target for the drug to work, which may be influenced by the type of tumour, sex or ethnicity. The healthcare provider will first test for these proteins before choosing the appropriate medication and dosing.​²​ 

Types  

The two main categories of targeted therapy are: 

• Monoclonal antibodies: like bevacizumab (Avastin) and rituximab (Mabthera), they can be used to treat other conditions like rheumatoid arthritis  
• Small molecule drugs: these drugs bind to cancer cells to interrupt their function​²​ 

Chemotherapy versus targeted therapy  

Standard chemotherapy kills rapidly dividing cancer cells, but it can also kill our rapidly dividing normal cells found in the skin, blood, gut, etc., resulting in numerous side effects that are capable of causing a significant impact in the overall health. On the other hand, targeted therapy is usually less harmful to normal cells leading to milder side effects and more tolerable treatment. Targeted therapy is also able to target specific types of cancer cells that proved to be resistant to conventional chemotherapy due to certain molecular structures.​³​  

Although chemotherapy remains the standard treatment option for most types of cancers, doctors may need to use a combination of both therapies to achieve the best possible outcome.​³​ 

Side effects of targeted therapy  

Side effects of targeted therapy usually happen in the first days or weeks of treatment; though they may present later. Symptoms are mild to moderate in most of the cases, and vary from person to person. They result from the direct effect of the drug on healthy cells and can affect a wide range of body organs.  

Common side effects 

Skin problems 

Skin conditions are one of the most encountered problems you may face if you are prescribed a targeted drug, and they are able to negatively affect your physical and emotional wellbeing if not dealt with properly.​⁴​ Luckily, these reactions were shown to be linked to treatment success in many cases.​²​ 

They appear in the form of: 

• Rash: may appear as small bumps that can be red or painful causing discomfort. They appear most in the face, chest and upper trunk. It’s usually self-limited; however, it can become infected and more widespread  
• Dry skin: some targeted therapies may lead to skin dryness, which, if severe, can lead to skin cracking and increased risk of infection  
• Itching: itching is an uncomfortable side effect that can present on its own or in accompany skin rash and dryness  
• Hair changes: patchy hair loss and colour change are disturbing complications of targeted therapy that appear after 2-3 months of treatment. Fortunately, it is reversible and resolves after the discontinuation of treatment⁴​ 

Management of skin complications:  

Your doctor can help you manage your skin side effects by recommending: 

• The use of emollients to reduce itching and dryness 
• Avoidance of irritants and excessive sun exposure  
• Prescribing medications like topical steroids and antibiotics to treat troublesome symptoms or infection in more severe cases​⁵​ 

Diarrhoea  

Diarrhoea or loose stools is another frequent and early side effect of targeted therapy. Its severity can range from mild to serious, potentially warranting hospitalisation, depending on the specific agent used as well as the dose. If prolonged, it can lead to nutritional deficiencies, dehydration and eventually dose reduction or drug discontinuation that may have a negative effect on cancer prognosis.  

Other related digestive issues include:​^6,7​  

• Nausea 
• Vomiting 
• Appetite changes   

Management: 

Targeted therapy-induced diarrhoea is managed by reducing the dose of the causative drug and by the use of antidiarrheal medications like loperamide.​⁶​   

Fatigue   

Fatigue is a very frequent symptom facing people treated for cancer. It results from multiple factors including the cancer itself, coexisting conditions like anaemia and depression, or as an adverse effect of therapy. For instance, targeted therapy can induce hypothyroidism (underactive thyroid gland) which is a well-known cause of fatigue.  

You may complain of tiredness, lack of energy and muscle weakness leading to difficulty carrying out daily activities. You should report these symptoms to your doctor so they can search for the possible cause and recommend the most suitable management plan.⁸​ 

Mouth sores  

Targeted therapy can result in painful sores and inflammation of the oral cavity (stomatitis) affecting the tongue, cheek lining, and palate. It is usually mild but the pain may interfere with your food intake.⁹​ 

Management  

Good oral care with regular tooth brushing and flossing, along with the use of saline or baking soda rinses is essential to prevent oral injury and promote repair.  

When sores are present, it is advised to use pain killers and to avoid irritating food like acidic and spicy meals.​⁹​ 

Less common but serious side effects 

Heart and vascular problems 

Certain targeted therapies, like angiogenesis inhibitors, do interfere with blood vessels formation process and have the potential to cause: 

• Heart damage which can lead to reduced heart function and disturbance of heart electricity  
• High blood pressure 
• Increased blood clotting resulting in thrombosis 
• Bleeding and bruises  

Symptoms like shortness of breath, increased tiredness, vomiting of blood or leg swelling should promptly be reported to the doctor to exclude or confirm heart and vascular system complications.¹⁰​ 

Liver  

Some targeted therapies, like imatinib, are known to cause serious liver toxicity which may result in treatment interruption. Symptoms like yellow eye and skin discoloration along with dark urine may not appear in the early course of toxicity unless the damage becomes profound. Therefore, people using such drugs must be monitored regularly by measuring the liver enzymes and function, and should minimise their intake of other liver-toxic substances like alcohol and paracetamol.⁶​ 

Lung problems  

Lung inflammation (pneumonitis) and toxicity can result from the use of certain targeted cancer treatments as well as from infection due to the weakened immunity common in cancer patients. It leads to symptoms like: 

• Cough 
• Difficulty breathing 
• Chest pain 

Reporting symptoms early prevent the progression to more serious complications including respiratory failure. The oncologist may reduce the dose or stop the medication and prescribe medications to reduce the inflammation like steroids.​¹¹​ 

Infusion reaction  

It is a kind of inflammatory reaction that happens during or after the administration of the drug leading to: 

• Fever  
• Chills  
• Drop in blood pressure  
• Increased heart rate  

You should inform your healthcare team if you developed any of these symptoms.  

Immune related adverse events  

Some targeted therapies like ipilimumab can produce a form of immune dysregulation causing overwhelming inflammation and autoimmunity in which the body starts to attack its own healthy cells.¹¹​ 

Managing side effects 

specific measures must be taken to guarantee optimal benefit from targeted therapy while minimising and addressing side effects, such as:  

Prevention strategies 

Health care providers will identify individuals at risk of developing side effects and provide their advices like: 

• Frequent use of emollients and avoidance of irritants to reduce skin problems 
• Good hydration to prevent dehydration from diarrhoea  
• Good oral hygiene  

Treating symptoms 

Individuals receiving targeted therapy should be able to identify bothersome and serious side effects that need prompt medical attention. Your health team will investigate possible causes and provide the appropriate management specific for each symptom that may include dose reduction or drug substitution.  

Regular checkup  

Regular blood tests and follow-up is essential to detect early side effects that may pass unnoticed until they progress to more advanced stages.  

Multidisciplinary collaboration 

Addressing side effects of targeted therapy requires multidisciplinary effort to achieve the optimal outcome. Nurses, primary care doctors, specialist oncology teams, mental health professionals are just a few from the many teams involved in this collaborative work. Each plays a critical role in assessing, detecting and educating and supporting patients with their families.^12,13​ 

Impact on quality of life  

Although targeted therapy was proven to improve the overall survival and improved the prognosis, it means that people with cancer will live longer to experience more side effects of their cancer medications which have a negative impact on their daily life.²​ 

For example, studies have shown that people with targeted therapy skin problems like face rash or dryness had lower quality of life as they reported physical discomfort like pain and skin sensitivity, increased worry and stress about the physical appearance or the development of more side effects, depression and withdrawal.¹⁴​ 

Therefore, it is essential to tackle these issues to ensure effective cancer control while minimising treatment-related complications.   

Summary  

Targeted therapy is a type of cancer treatment which attacks specific components responsible for promoting the growth and spread of cancer cells. Unlike chemotherapy, it tends to have milder side effects; though some can be serious. Common side effects include skin rash and dryness, diarrhoea and fatigue while severe but less frequent complications are heart, lung and liver toxicity. Multidisciplinary collaboration, regular follow-up, patient education and support are necessary to improve the overall wellbeing of individuals receiving targeted therapy.