Oncology

Cancer will affect approximately one-in-two people in Ireland at some point in their lives. Therefore, screening and early detection are increasingly important. On completion of this module, it is expected the reader will have an enhanced understanding of cancer classifications, staging, diagnosis and treatment. Various therapies are also discussed, including the pivotal role of the pharmacist.

Oncology is the branch of medicine that specialises in the study of cancer, including its prevention, diagnosis, and treatment. Cancer is defined as a large group of diseases characterised by the abnormal and uncontrollable growth of cells, with the potential to invade or spread to other organs in the body. It is one of the leading causes of morbidity and mortality globally, ranking as the second-leading cause of death worldwide, behind heart disease.

Cancer accounts for an estimated 9.6 million deaths each year globally – approximately one in every six deaths. More than one-in-two people in Ireland will develop some form of cancer in their lifetime, with prostate, breast, bowel, lung, and skin cancers the most common types.

Survival rates for many cancers have improved in recent years due to earlier detection and improved treatments. Pharmacists are integral members of the multidisciplinary cancer team, contributing to medication management, patient education, and supportive care.

This module will provide an in- depth exploration of oncology from a pharmacist’s perspective, including the pathophysiology, classification, staging, risk factors, prevention, screening, clinical presentation, treatment modalities, and the evolving role of pharmacists in cancer care.

Pathophysiology

Cancer is characterised by uncontrolled cell proliferation due to genetic mutations that disrupt normal cell cycle regulation. There are alterations in genes that regulate cell growth and differentiation in cancerous cells – oncogenes and tumour suppressor genes. Oncogenes promote cell division, while tumour suppressor genes inhibit cell division.

These genetic changes disrupt normal regulatory pathways, allowing cells to evade apoptosis (programmed cell death), sustain proliferative signalling, and resist growth suppressors. Angiogenesis is a trait of cancer, where new blood vessels are formed to supply oxygen and nutrients, facilitating further expansion.

Furthermore, cancer cells may develop the ability to invade surrounding tissues and metastasise to other organs in the body. This can occur via the blood or the lymphatic system and is a major cause of cancer-related mortality. The process of metastasis involves the invasion

of nearby tissue, entry into blood vessels or lymph nodes, circulation around the body, invasion of new tissue, and formation of a new metastatic tumour. Understanding the pathophysiology is important to comprehend treatment modalities and develop targeted therapies.

Classification

Cancer can be broadly classified into categories based on tissue site of origin:

Carcinomas: Originate in the epithelial cells of the skin, gastrointestinal tract, internal organs, and glands. They tend to form solid tumours and include colorectal cancer, lung cancer, prostate cancer, and breast cancer.

Sarcomas: Originate in connective tissues – tissues that connect and support organs and body structures. They can develop in muscle, fat, bone, tendons, blood vessels, and lymph vessels.

Leukaemia: Cancers of the blood- forming tissues, leading to the production of abnormal white blood cells. Leukaemia can be further classified into acute lymphocytic leukaemia, chronic lymphocytic leukaemia, acute myeloid leukaemia, and chronic myeloid leukaemia.

Lymphomas: Cancers that originate in the lymphatic system and include Hodgkin lymphoma and non-Hodgkin lymphoma.

Cancer staging

Staging refers to the extent of cancer spread, including the tumour size, the degree of lymph node involvement, and the presence of metastases. Accurate staging is essential for determining prognosis and guiding treatment decisions. The most commonly used cancer staging system is the TNM classification:

• T (tumour): Size and extent of the primary tumour.
• N (nodes): Involvement of localised lymph nodes.
• M (metastasis): Presence of metastases.

Risk factors

Several risk factors contribute to cancer development. It is estimated that 80-to- 90 per cent of cancers are attributable to genetic mutations related to external environmental factors (carcinogens), with the remainder due to inherited genetic factors.

Tobacco smoke, including second- hand smoke, is one of the leading causes of cancer-related deaths worldwide, particularly lung, mouth, and throat cancers. Alcohol consumption is a risk factor for many cancer types, including those of the liver, oesophagus, pharynx, larynx, colorectum, and breast. The risk increases with the amount of alcohol consumed.

Physical inactivity, poor diet, and obesity are also major contributors. Physical inactivity not only contributes to obesity but independently raises the risk of several cancers. Obesity is associated with increased risk of cancers of the oesophagus, colorectum, breast, endometrium, and kidney.

Environmental exposure to carcinogens also plays a significant role. Ultraviolet (UV) radiation
from sunlight is associated with an increased risk of skin cancers. Ionising radiation, whether from medical imaging or natural sources, can increase the risk of various cancers, particularly leukaemia, thyroid, lung, and breast cancers. Air pollution has been linked to lung cancer, while physical agents such as asbestos increase the risk of mesothelioma and other cancers. Infections also contribute to cancer development. Human papillomavirus, Epstein-Barr virus, and hepatitis B and C viruses are associated with an increased risk of different cancers. Hormones can also influence cancer risk. Higher levels of oestrogen and progesterone are linked to breast, endometrial, and ovarian cancers, while testosterone may contribute to testicular and prostate cancers. Educating patients about modifiable risk factors and promoting healthy lifestyle choices is essential in cancer prevention.

Cancer prevention

Cancer prevention involves taking active measures to decrease the risk of developing cancer, encompassing primary, secondary, and tertiary strategies.

Primary prevention focuses on reducing exposure to risk factors. This includes avoiding tobacco smoke and excessive alcohol use, engaging in regular physical activity, maintaining a healthy weight, avoiding environmental carcinogens, and minimising UV light exposure. Vaccination plays an important role, with vaccination against human papillomavirus and hepatitis significantly reducing the risk of related cancers.

Secondary prevention involves early detection through screening programmes, as outlined in a following paragraph. Early diagnosis often results in more effective treatment and improved clinical outcomes.

Tertiary prevention refers to the management of diagnosed cancer to reduce complications, prevent recurrence, and improve patients’ quality of life. It includes treatment interventions such as surgery, chemotherapy, and radiotherapy, as well as rehabilitation, palliative care, and monitoring for metastases.

Pharmacists can contribute to cancer prevention by counselling patients on lifestyle modifications, administering vaccines, participating in public health campaigns, and providing support to already diagnosed patients.

Cancer screening

Secondary prevention involves the early detection of cancer through screening programmes. This involves identifying precancerous lesions and taking intervention measures to prevent disease progression to malignancy. Early detection through screening improves treatment outcomes.

In Ireland, cancer screening is provided by the National Screening Service, which offers screening for cervical, breast, and colorectal cancers. Screening for breast cancer is available through the Health Service Executive’s (HSE) programme BreastCheck for women aged 50-to-70 years.

A cervical screening test and human papillomavirus test are available for women aged 25-to-65 years, with the intervals between tests varying depending on an individual’s age. Colorectal cancer screening is available for individuals aged 59- 70 years and involves a home test kit, with a follow-up colonoscopy if necessary. Pharmacists can educate patients about the importance of cancer screening, identify individuals eligible for screening, and facilitate referrals to appropriate services.

Clinical presentation and symptoms

There are several types of cancer that can cause a wide range of signs and symptoms. Cancer symptoms may vary widely depending on the type and stage of cancer. Symptoms may be specific to certain body areas, or more generalised. Pharmacists should be vigilant in recognising potential early warning signs and counselling patients to seek medical evaluation promptly. Warning symptoms that should be evaluated include:

• Unexplained weight loss;
• Heavy night sweats;
• Fatigue;
• Loss of appetite;
• Unexplained and persistent
• Changes in bowel or bladder habits;
• Abnormal bleeding or discharge;
• Unusual lump or swelling;
• Difficulty swallowing or persistent indigestion;
• Skin changes.

Diagnosis

Cancer may be initially recognised through screening programmes or the presentation of signs and symptoms. These methods do not provide a definitive diagnosis, and further investigations are required. Patients are typically referred for a variety of investigative procedures depending on the suspected cancer type.

The types of tests may depend on which type of cancer is suspected.

Medical imaging tests such as x-rays, MRI (magnetic resonance imaging), and CT (computed tomography) scans can help identify tumour masses. Endoscopy may be used to visualise abnormalities within the body, and blood tests can detect tumour markers indicative of cancer. A definitive diagnosis typically requires a biopsy – a sample of tissue examined under a microscope to assess for the presence of cancer cells.

Treatment

Cancer treatment is multifaceted, with the objectives to cure the disease, control its progression, or alleviate symptoms to improve quality of life. Treatment selection depends on factors including the type of cancer, stage, patient health status, and treatment objectives. The main treatment modalities include surgery, radiation therapy, chemotherapy, hormonal therapy, and targeted therapy.

In addition to curative treatment, supportive care is an essential aspect of cancer management. Common symptoms and complications – such as pain, nausea, vomiting, neutropaenia, mucositis, and thromboembolic risk – require proactive management. Palliative care also plays a crucial role, focusing on symptom relief, pain management, and enhancing
the quality of life for patients with advanced or terminal cancer.

Surgery

Surgery is one of the most common and effective treatments for cancer, particularly in early-stage disease. The primary objective of surgery is to remove localised tumours, which may include surrounding healthy tissue, to reduce the risk of recurrence. Surgery can often be curative in localised cancers, where the entire tumour and involved lymph nodes can be completely removed.

Examples of surgical treatment include mastectomy or lumpectomy for breast cancer, lung surgery for non-small cell lung cancer, and prostatectomy for prostate cancer. Debulking surgery is performed to reduce the size of a tumour, typically to enhance the effectiveness of other treatment modalities such as chemotherapy or radiation therapy. Palliative surgery may be used to relieve symptoms – such as obstruction, pain, or bleeding – in advanced stages of cancer, and may also prolong life. Reconstructive surgeries aim to restore function or appearance, with breast reconstruction following mastectomy an example.

Recovery from surgery can be complex and requires involvement from many healthcare professionals within the multidisciplinary team. Physiotherapists assist with breathing exercises and mobility, while dietitians support optimal nutrition during recovery. Surgical care also includes pre- and postoperative medication management, such as prophylactic antibiotics, pain control, antiemetics, and thromboprophylaxis. Pain is a common postoperative concern and is managed with analgesics such as paracetamol, non-steroidal anti-inflammatory drugs (NSAIDs), opioids, and adjuvants, following the World Health Organisation analgesic ladder. Constipation may occur due to reduced mobility or opioid use and should be appropriately managed with laxatives. Although surgery may be effective in certain cases, it may not be suitable if the cancer has metastasised or if a patient’s overall health status precludes safe anaesthesia and recovery. In such cases, alternative treatment modalities are considered.

Radiation therapy

Radiation therapy is an important treatment option in oncology. It uses high-energy radiation, such as x-rays, gamma rays, or charged particles, to damage the deoxyribonucleic acid (DNA) of cancerous cells, thereby inhibiting their ability to grow and divide. Radiation therapy may be used as monotherapy
or in combination with other treatment options, depending on the cancer type and stage. The goal of radiation therapy is to deliver treatment that is as localised as possible, targeting cancerous tissue while minimising damage to surrounding healthy cells. There are two primary types of radiation therapy:

External beam radiation therapy delivers radiation from an external machine, targeting the tumour site precisely.

Pharmacists contribute by ensuring the safe and appropriate dispensing of supportive therapies

Internal radiation therapy involves the placement of radioactive sources inside or near the tumour, which offers localised treatment with minimal damage to surrounding tissues.

Adverse effects are associated with radiation therapy and depend on the dose, site, and schedule of the therapy. Common adverse effects include fatigue, hair loss, mucositis, nausea, vomiting and red, irritated, blistered, dry, or itchy skin. Although radiation therapy does not involve drug administration directly, medication plays an important supportive role.

Pharmacists contribute by ensuring safe and appropriate dispensing of supportive therapies, such as analgesics, antiemetics, corticosteroids, antibiotics, and topical agents, to manage adverse effects and support adherence. In addition, pharmacists may monitor for long-term complications and counsel patients on skin care, oral hygiene, and nutritional support, depending on the site of radiation.

Chemotherapy

Chemotherapy involves the use of cytotoxic drugs to eliminate cancer cells by disrupting their ability to grow and divide. Chemotherapy may be administered with the intent to cure disease, control progression, or palliatively to improve quality of life. It is often used in combination with other treatment modalities, such as surgery or radiation therapy, as part of a multimodal approach. Chemotherapy is an important aspect of cancer treatment, with its success depending not only on tumour biology, but also on the management of adverse effects. Chemotherapeutic agents typically target rapidly-dividing cells, which is characteristic of many cancers. These drugs commonly work by damaging DNA, interfering with nucleotide synthesis, or disrupting the process of cell division. Some key classes of chemotherapeutic drugs include:

• Alkylating agents: Cyclophosphamide, cisplatin. Antimetabolites: 5-fluorouracil, methotrexate, capecitabine.
• Topoisomerase inhibitors: Etoposide, irinotecan, doxorubicin.
• Antimicrotubule agents: Paclitaxel, vincristine.
• Cytotoxic antibiotics: Doxorubicin, bleomycin.

However, due to the non-specific nature of these drugs, healthy proliferative tissues such as bone marrow, gastrointestinal mucosa, and hair follicles are often affected, resulting in a range of adverse effects. Myelosuppression is a common adverse effect, which can lead to neutropaenia, anaemia, and thrombocytopaenia. Other frequent side-effects include nausea, vomiting, mucositis, diarrhoea, alopecia, and peripheral neuropathy.

Long-term risks may include infertility, cardiotoxicity, and teratogenicity. Supportive medications play a crucial role in managing these adverse effects. Common examples include:

• Antiemetics (ondansetron, metoclopramide, aprepitant, cyclizine, domperidone, and prochlorperazine) are used to prevent and treat nausea and vomiting.
• Proton pump inhibitors (omeprazole, pantoprazole, lansoprazole, and esomeprazole) are used for gastrointestinal protection.
• Analgesics (paracetamol, NSAIDs, and opioids) can be used to relieve cancer-related pain.
• Allopurinol is a xanthine oxidase inhibitor used prophylactically to prevent tumour lysis syndrome.
• Prophylactic antimicrobials (trimethoprim/sulfamethoxazole, fluconazole, aciclovir) are used to reduce infection risk due to the immunosuppressive nature of chemotherapy.
• Corticosteroids (dexamethasone, prednisolone) may work as an anti- inflammatory, antiemetic, appetite stimulant or to prevent allergic reactions. Growth factors:
• Filgrastim is a recombinant granulocyte colony-stimulating factor (G-CSF) used to stimulate neutrophil production in patients with neutropaenia.
• Epoetin alfa and darbepoetin alfa are erythropoiesis-stimulating agents (ESAs) used to manage chemotherapy-induced anaemia.

Targeted therapy

Targeted cancer therapies offer a more selective approach to treatment by focusing on specific molecular targets involved in tumour growth and progression. Unlike conventional chemotherapy, which affects all rapidly dividing cells, targeted therapies aim to block the growth and spread of cancer cells by interfering with the specific molecules essential for carcinogenesis and tumour development. This targeted mechanism often results in fewer adverse effects. Targeted therapies are broadly classified into two categories: Monoclonal antibodies, and small molecule inhibitors.

Monoclonal antibodies are large protein molecules designed to bind to specific antigens expressed on cancer cells. They work by blocking receptor activity, marking cancerous cells for immune destruction, or delivering cytotoxic agents directly to tumours. Trastuzumab targets HER2 receptors in breast cancer and can be administered in combination with chemotherapeutic agents for gastric cancers. Cetuximab binds epidermal growth factor receptor (EGFR) and is used in colorectal and head and neck cancers. Bevacizumab targets vascular endothelial growth factor (VEGF) to inhibit angiogenesis
in various solid tumours. Monoclonal antibodies are typically administered intravenously and may cause infusion- related reactions.

Small molecules inhibitors are typically administered orally and penetrate cells to disrupt intracellular signalling pathways. Tyrosine kinase inhibitors (TKIs) block the enzyme activity of tyrosine kinases, which are responsible for regulating growth signals in cancer cells. Imatinib and dasatinib are used to treat chronic myelogenous leukaemia, while erlotinib and gefitinib target EGFR in non-
small cell lung cancer. Sorafenib is a multi-kinase inhibitor used in liver and renal cancers. Other small molecule inhibitors target non-kinase pathways, with venetoclax used to treat chronic lymphocytic leukaemia and acute myeloid leukaemia by promoting apoptosis of cancer cells.

Although generally associated with a more favourable side-effect profile than traditional chemotherapy, targeted therapies are not without limitations. Drugs are often difficult and expensive to develop. Resistance to targeted therapies remains a key challenge, which can be primary (no initial response) or acquired (loss of response over time). Mechanisms of resistance include secondary mutations, activation of alternative signalling pathways, or downregulation of the target receptor. Management strategies may involve switching to next-generation inhibitors or using combination regimens. There can also be adverse effects associated with the use of targeted therapy. Adverse effects vary depending on the specific agent and patient. Common adverse effects include liver dysfunction, nausea, vomiting, diarrhoea, and skin issues, with other potential adverse effect,s including hypertension, blood clotting abnormalities, impaired wound healing, fatigue, and mouth sores. Drug interactions are another important consideration, particularly with oral agents metabolised by CYP enzymes.

Hormonal therapy

Hormonal therapy is a targeted cancer treatment that works by blocking or reducing hormone levels that stimulate the growth of hormone-sensitive cancers. It is particularly effective in treating certain breast and prostate cancers that rely on hormones such as oestrogen or testosterone for tumour growth and proliferation.

Selective oestrogen receptor modulators (SERMs), such as tamoxifen, bind to oestrogen receptors and act as antagonists in breast tissue. They are effective in treating hormone receptor-positive cancer in pre-menopausal women and are also used for chemoprevention in high- risk individuals.

Aromatase inhibitors are effective in treating hormone receptor-positive breast cancer in postmenopausal women. Anastrozole, letrozole, and exemestane are examples of aromatase inhibitors that inhibit the enzyme aromatase, reducing peripheral oestrogen synthesis and slowing tumour progression.

Gonadotropin-releasing hormone (GnRH) analogues, such as leuprorelin and goserelin, suppress ovarian oestrogen production in premenopausal women by inducing a negative feedback mechanism on the pituitary gland. These are administered parenterally and may be used alone or in combination with other hormonal agents.

Hormonal treatment options for prostate cancer aim to reduce androgen levels or block their action. Antiandrogen agents, such as bicalutamide or enzalutamide, inhibit androgen receptors on prostate cancer cells, blocking the effects of testosterone. They can be used as monotherapy or combined with GnRH analogues. Similarly to treating breast cancer, GnRH analogues work in prostate cancer by suppressing testosterone production in the testes due to a negative feedback response of continuous stimulation of the pituitary gland.

Hormonal therapies may be used as monotherapy or in combination with other treatment modalities, depending on the cancer type, stage, and patient factors. Although generally better tolerated than cytotoxic chemotherapy, hormonal therapies are associated with specific adverse effects, which vary by drug, dose, and patient characteristics. Hot flushes, night sweats, fatigue, sexual dysfunction, fertility issues, mood changes, and weight changes are commonly-observed adverse effects. Erectile dysfunction and gynecomastia are potential adverse effects in males, while vaginal dryness, discharge, and irritation, as well as menstruation changes, are common in females. Finally, long-term use may also increase the risk of other conditions, including cardiovascular disease, osteoporosis, and secondary cancers.

Role of the pharmacist

Pharmacists have a crucial role to play in cancer management in the community. As one of the most accessible healthcare professionals, pharmacists often serve as the first point of contact for patients and are widely trusted for their clinical expertise.

In cancer prevention, pharmacists are involved in health promotion and education, including counselling on risk- reduction strategies such as smoking cessation and healthy lifestyle choices. They also raise awareness of early warning signs of cancer and facilitate referral to appropriate medical services when necessary.

Additionally, pharmacists may administer human papillomavirus vaccines, contributing to primary prevention efforts. The pharmacist’s role has expanded beyond traditional dispensing to a patient-centered approach. Pharmacists provide counselling on treatment regimens, explain the mechanism and purpose of prescribed therapies, and address concerns regarding adverse effects, drug interactions, and supportive care measures. Pharmacists are also well-positioned to monitor treatment adherence, identify non-compliance, and implement strategies to support medication-taking behaviour. This is especially important in complex cancer regimens where maintaining therapeutic efficacy is critical. Beyond clinical duties, pharmacists offer emotional and practical support to patients and their families, helping them understand and manage the challenges of a cancer diagnosis and its treatment. Finally, pharmacists are integral members of the multidisciplinary healthcare team, collaborating with other healthcare professionals to optimise clinical outcomes.