High grade serous epithelial ovarian cancer includes cancer of the fallopian tubes and cancer of the peritoneum. Niraparib is used on its own for the ‘maintenance’ treatment of patients who have relapsed disease. The medicine is given after treatment with platinumbased medicines, when the tumour is diminishing in size or has completely disappeared. Niraparib blocks the action of enzymes called PARP-1 and PARP-2, which help to repair damaged DNA in cells when the cells divide to make new cells. By blocking PARP enzymes, the damaged DNA in cancer cells cannot be repaired, and, as a result, the cancer cells die. Niraparib has been shown to increase the time patients lived without their disease getting worse in one main study involving 553 patients. Patients in the study had high grade serous epithelial ovarian cancer, including fallopian tube or peritoneal cancers. Patients had undergone treatment with two or more platinum-based therapies, with a lasting response (the cancer had not progressed for at least 6 months) before the last platinum-based therapy. Patients treated with niraparib lived on average 11.3 months without their disease getting worse compared with 4.7 months in patients treated with placebo. The most common side effects with Zejula are nausea, thrombocytopenia, tiredness and weakness, anaemia, constipation, vomiting, abdominal pain, neutropenia, insomnia, headache, lack of appetite, nasopharyngitis, diarrhoea, dyspnoea, hypertension, dyspepsia, back pain, dizziness, cough, urinary tract infection, joint pain, palpitations and dysgeusia. Serious side effects include thrombocytopenia and anaemia.