A Study to Investigate Biomarker Effects of Pre-Surgical Treatment With DNA Damage Repair (DDR) Agents in Patients With Head and Neck Squamous Cell Carcinoma (HNSCC).

Pertinent Inclusion Criteria: * Provision of informed consent * Aged at least 18 years * Eastern Cooperative Oncology Group (ECOG) performance status 0,1 or 2 with no deterioration over the previous 2 weeks and an estimated life expectancy of greater than 12 weeks * Treatment naïve HNSCC either newly diagnosed, or a second tumour at more than two years after successful treatment of the primary cancer, suitable for surgical resection that is likely to be followed by radiotherapy and/or chemotherapy after surgery. Patients who are suitable for radical chemoradiation without surgery are eligible if they are willing to undergo an on-treatment biopsy (FNA samples are not acceptable, specimens must be core or surgical biopsy). * Females must be using adequate contraceptive measures, must not be breast feeding and must have a negative pregnancy test prior to start of dosing if of child-bearing potential or must have evidence of non-child-bearing potential * For the duration of the study and for 6 months after the last study drug administration, sexually active male patients must be willing to use barrier contraception i.e., condoms with all sexual partners * No previous systemic cancer treatment or radiotherapy for the current malignancy * Provision of genetics research informed consent Pertinent Exclusion Criteria: * Involvement in the planning and/or conduct of the study * Previous treatment with a DDR agent * Participation in another clinical study with an investigational product during the last 21 days or 5 half-lives of the investigational product, whichever is longer * Receiving, or having received during the week prior to first dose, corticosteroids at a dose \> 10 mg prednisone/day or equivalent for any reason * Known hypersensitivity or contraindication to any of the investigational agents or their excipients * Small molecule investigational medicinal products (IMPs) within 28 days prior to first dose; biological IMP within 42 days prior to first dose * Receiving, or received, concomitant medications, herbal supplements and/or foods that significantly modulate Cytochrome P450 3A4 (CYP3A4) inhibitors or moderate Cytochrome P450, family 3, subfamily A (CYP3A) inhibitors, strong CYP3A inducers or moderate CYP3A inducers * Impaired hepatic or renal function,inadequate bone marrow reserve or organ function * Cardiac dysfunction defined as: Myocardial infarction within six months of study entry, New York Heart Association (NYHA) Class II/III/IV heart failure, unstable angina, unstable cardiac arrhythmias or reduced LVEF \< 55% * Any of the following cardiac criteria: Mean resting corrected QTc interval using the Fridericia formula (QTcF) greater than 450 msec/male and greater than 470 msec/female or congenital long QT syndrome, clinically important abnormalities in rhythm, conduction or morphology of resting electrocardiography (ECG), factors that increase the risk of QTc prolongation or risk of arrhythmic events, patients at risk of brain perfusion problems, relative hypotension (\<100/60 mm Hg) or clinically relevant orthostatic hypotension (\>20 mm Hg), uncontrolled hypertension * Any other malignancy (i.e., non-HNSCC) which has been active or treated within the past three years (except cervical intra-epithelial neoplasia and non-melanoma skin cancer) * Patients unable to swallow orally administered medication and patients with gastrointestinal disorders likely to interfere with absorption of the study medication * Patients considered a poor medical risk due to a serious, uncontrolled medical disorder, non-malignant systemic disease or active, uncontrolled infection * Judgement by the Investigator that the patient should not participate in the study * Patients with myelodysplastic syndrome (MDS)/acute myeloid leukaemia (AML) or with features suggestive of MDS/AML * Previous allogenic bone marrow transplant or double umbilical cord blood transplantation (dUCBT) * Non-leukocyte depleted whole blood transfusion within 120 days of the date of patient's start on the study