Targeted Therapy Side Effects: — What Is Normal and What Needs a Call

EGFR inhibitors are used most commonly in lung cancer with an EGFR mutation, and their most prominent effect is on the skin. An acneiform rash — a pimple-like eruption across the face, chest, and back — appears in many patients within the first two weeks. Dry skin, paronychia (inflammation around the fingernails and toenails), and diarrhoea are also common. Hair may become wavy or brittle with longer-term use. Most skin effects are managed with topical treatments and oral antibiotics — ask your team for a skin care protocol before you start, not after the rash has already appeared. A rash that is infected, blistered, or severe enough to affect sleep needs reporting promptly.

HER2-targeted treatments are used in breast and gastric cancers with HER2 overexpression. Trastuzumab carries a risk of cardiac toxicity — specifically a reduction in the heart's pumping function — which is why regular echocardiograms are a standard part of monitoring throughout treatment. Most people do not develop symptoms, but breathlessness or ankle swelling should be reported before your next scheduled scan rather than waited out. Lapatinib, taken as a daily oral tablet, causes diarrhoea more prominently than the intravenous agents. Infusion-related reactions — chills, flushing, or mild fever during the drip — can occur with trastuzumab on the first dose and are managed by slowing the infusion; tell the nurse immediately if you feel unwell during any infusion.

These drugs reduce the blood supply tumours depend on, and their side effects reflect that mechanism. Blood pressure rises in a proportion of patients and needs regular home monitoring — your team will give you a target range to stay within. Hand-foot syndrome is particularly prominent with oral VEGFR inhibitors: the palms and soles become red, tender, and may peel in areas exposed to pressure or friction. Fatigue and diarrhoea are also common. Because these agents impair wound healing, any planned procedure — including dental extractions — must be discussed with your oncologist well in advance. Bleeding complications are a real risk: report blood in stool, urine, or sputum the same day rather than waiting to see if it settles.

BCR-ABL inhibitors are the standard treatment for chronic myeloid leukaemia. Imatinib, the original agent, commonly causes fluid retention — puffiness around the eyes in the morning, ankle swelling, and gradual weight gain. Nausea is manageable by taking the tablet with a meal and a full glass of water. Muscle cramps, particularly at night, affect some patients. Dasatinib carries a specific risk of pleural effusion — fluid collecting around the lungs — causing progressive breathlessness that must be reported without delay. Nilotinib is associated with effects on the heart's electrical rhythm, which is why ECG monitoring is part of its standard follow-up protocol. All agents in this class interact with many common medicines, including antacids — tell your team about everything you take.

CDK4/6 inhibitors are used in hormone receptor-positive breast cancer, almost always alongside an endocrine therapy. Their most clinically important side effect is a drop in white blood cell count (neutropenia), which is why blood tests are scheduled frequently during the first months of treatment. The neutropenia may cause no noticeable symptoms — you can feel entirely well — but the count still needs to be confirmed as safe before each cycle, because a low count raises infection risk. Diarrhoea is more pronounced with abemaciclib than with the other agents in this class. Fatigue and mild nausea are common early on and often settle over the first two months. If you develop a fever while on a CDK4/6 inhibitor, treat it as urgent regardless of how mild it seems.

BRAF and MEK inhibitors are used in melanoma with a BRAF mutation and in some other BRAF-mutated cancers. Fever is among the most common and disruptive side effects when dabrafenib and trametinib are used together — episodes of high temperature that resolve within hours are typical and manageable, but fever alongside low blood pressure, confusion, or severe shaking needs urgent review rather than home management. Skin sensitivity to sunlight is marked with BRAF inhibitors: ordinary outdoor exposure can cause severe burn-like reactions, so long sleeves, a hat, and a high-SPF sunscreen applied daily are essential. Secondary skin lesions, including keratoacanthomas, can develop and should be assessed by a dermatologist promptly rather than left to the next scheduled oncology visit. Joint pain, fatigue, and headache are also commonly reported.