Breast cancer is the most common malignancy affecting women in the UK, with more than 55,000 new cases diagnosed annually (Cancer Research UK, 2023). Unsurprisingly, claims arising from delayed diagnosis or substandard management of breast cancer are among the most frequent forms of oncology-related clinical negligence litigation. For solicitors, a clear grasp of how the courts analyse breach of duty and causation in this context is essential. Below, we will discuss how errors in imaging, clinical assessment, or treatment may constitute a breach of duty, and how delays in diagnosis or management can affect staging, prognosis, and survival when causation is under consideration.

Breach of Duty

A breach occurs when the care provided falls below the standard expected of a reasonably competent practitioner in the same specialty. In breast cancer claims, breaches most commonly arise from failures to refer, misinterpretation of imaging, misreporting of pathology resulting in inappropriate treatment, or insufficient follow-up in patients at higher risk.

For instance, a GP who fails to make a two-week wait referral despite a patient presenting with a persistent, hard lump is unlikely to withstand scrutiny, particularly given the clarity of NICE guidance on “red flag” symptoms. Likewise, a radiologist who overlooks an abnormal lesion on mammography, or a pathologist who erroneously reports a malignant biopsy as benign, may be found negligent.

The established legal tests apply: Bolam v Friern Hospital Management Committee [1957] holds that a clinician is not negligent if their actions accord with a responsible body of medical opinion. However, Bolitho v City and Hackney HA[1998] refined this by requiring that the body of opinion must withstand logical scrutiny. In practice, clear guideline breaches or objectively unreasonable interpretations of imaging or pathology often satisfy the threshold for breach.

Causation

Causation is often more contested than breach. The central question is: but for the delay or error, would the claimant’s outcome have been materially better? The analysis typically considers three interrelated issues:

• Stage progression: Did the tumour advance from a small, operable lesion to one with nodal involvement or locally advanced disease during the delay?

• Prognosis: Did the delay reduce the claimant’s statistical chance of cure or survival at five or ten years?

• Treatment burden: Even if survival was not altered, did the delay result in more aggressive interventions, such as mastectomy instead of lumpectomy, or chemotherapy instead of endocrine therapy?

Courts usually apply the “material contribution” test: if the delay had more than a negligible effect on the outcome, causation may be established. Crucially, this means that causation can succeed even where ultimate survival is unaffected, provided there is evidence of avoidable treatment burden or quality-of-life impact.

The Impact of Delay

The consequences of diagnostic delay are best understood in terms of tumour stage. Prognosis in breast cancer correlates strongly with tumour size, nodal involvement and metastatic spread. A Stage I tumour (<2cm, node-negative) carries a five-year survival exceeding 90%, while Stage III disease with nodal spread reduces survival to around 70%. Even a delay of 6-12 months may allow measurable progression from Stage I to Stage II or III, with significant implications for treatment and outcome.

English law has historically resisted recognising “loss of a chance” claims below 50 per cent probability of survival, most notably in Gregg v Scott [2005]. However, where delay demonstrably reduces survival probability (for example, from 75% to 55%) claimants may still argue that they have been deprived of a substantial chance of cure. More frequently, causation arguments succeed where delay increases treatment intensity. A claimant who could have undergone breast-conserving surgery with endocrine therapy may, due to late diagnosis, require mastectomy, chemotherapy and nodal radiotherapy, with the attendant physical and psychological burdens.

Case Illustrations

Consider a 52-year-old woman whose screening mammogram reveals a spiculated density that is overlooked. Twelve months later, she presents with a 3.5cm invasive carcinoma with nodal involvement. Expert evidence supports that earlier detection would have confined disease to Stage I, treatable with lumpectomy and endocrine therapy. Instead, she required mastectomy and chemotherapy with reduced survival prospects. Here, both breach and causation are clear: the radiologist’s error directly worsened prognosis and increased treatment burden.

Another example involves a core biopsy misreported as benign. Only months later, with tumour progression, is malignancy confirmed. Whether causation is established depends on expert evidence as to whether the delay materially worsened outcome, but breach may be proven if the pathology fell below an acceptable standard.

Practical Points for Solicitors

Breast cancer claims are evidence-heavy, requiring meticulous preparation. Early instruction of specialist experts such as radiologists, breast surgeons, oncologists, and, where appropriate, pathologists, is essential in establishing both breach and causation. It is also important to distinguish cases requiring input from medical oncologists, who advise on systemic therapies such as chemotherapy, endocrine therapy, immunotherapy, and targeted agents, versus clinical oncologists, who oversee radiotherapy planning and delivery. Reconstruction of a detailed timeline from initial presentation through investigations to treatment then provides the framework against which tumour biology and growth rates can be assessed.

NICE guidelines on suspected cancer referral and breast cancer management are powerful tools for establishing breach, particularly in primary care. For causation, solicitors should remember that survival is not the only relevant outcome: avoidable mastectomy, chemotherapy, radiotherapy exposure and psychological harm are all material considerations. Finally, documentary evidence such as imaging, pathology slides and multidisciplinary team notes should be secured as early as possible, as they often provide the clearest evidence of substandard care.

Conclusion

Breast cancer litigation demands a sophisticated understanding of both medical and legal principles. Breach often arises from clear departures from guidelines or failures in clinical judgement, while causation requires careful analysis of tumour progression and treatment consequences. Even where survival is ultimately unaffected, claimants may succeed by demonstrating that delay necessitated more aggressive therapy or worsened quality of life. By working closely with medical experts and framing arguments around both prognosis and treatment burden, solicitors can present strong and persuasive claims on behalf of their clients.

Dr Vasileios Angelis

Medical Oncology Consultant

St Bartholomew’s Hospital

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References:

1. Cancer Research UK. Breast cancer statistics. Updated 2023. Available at: https://www.cancerresearchuk.org/health-professional/cancer-statistics/statistics-by-cancer-type/breast-cancer
2. National Institute for Health and Care Excellence (NICE). Suspected cancer: recognition and referral (NG12). 2021. Available at: https://www.nice.org.uk/guidance/ng12
3. Office for National Statistics (ONS). Cancer survival in England: adult, stage at diagnosis and childhood – patients followed up to 2020. London: ONS, 2022.
4. Bolam v Friern Hospital Management Committee [1957] 1 WLR 582.
5. Bolitho v City and Hackney Health Authority [1998] AC 232.
6. Gregg v Scott [2005] UKHL 2.
7. Gennari A, et al. Breast cancer prognosis according to stage: a population-based study. Breast Cancer Res Treat. 2018;169(3):591–602.
8. Richards MA, et al. Influence of delay on survival in patients with breast cancer: a systematic review. Lancet. 1999;353(9159):1119–1126.