Cancer Misdiagnosis: Red Flags Your GP Might Have Missed

A cancer misdiagnosis, where the diagnosis is missed or late, is one of the most serious forms of medical negligence in the NHS. It can have a devastating impact on an individual’s physical and emotional wellbeing, often leading to a significantly reduced quality of life, or even death.

Even so, being misdiagnosed by a GP is more common than many people realise. This guide is written for anyone who suspects that early warning signs of cancer were overlooked or dismissed. It is designed to help you understand how a cancer misdiagnosis might have happened — and the options available moving forward.

How Long Can Cancer Go Undetected?

The honest answer is, often much longer than most people realise. Cancer can grow silently for months, even years, before symptoms become obvious enough to prompt action. By that point, your treatment options may have changed significantly.

NHS Resolution’s October 2025 thematic review of 105 settled GP cancer negligence claims found that the average delay between symptoms first appearing and a cancer referral being made ranged from five to 16 months, depending on the type of cancer.

• Prostate cancer saw the longest average delay, at 16 months.
• Colorectal and lung cancers averaged nine and seven months, respectively.

In every single one of these cases, the patient had visited their GP three or more times before being referred.

Situations Anyone Affected May Recognise

A cancer misdiagnosis does not always hinge on a single, life-altering event. Frequently, it progresses through a series of smaller moments that, looking back, can be seen as adding up to something much bigger.

Here are a few common scenarios that come up when being misdiagnosed by a GP:

• Symptoms Were Misdiagnosed as Something Minor: Such as a persistent cough being treated as a chest infection, loose stools being described as irritable bowel syndrome, or blood in the urine being put down to a urinary tract infection. On some occasions, antibiotics may have been prescribed repeatedly, but without any further investigation.
• You Went Back, but Nothing Changed: You returned to your GP because you still did not feel well and the same treatment was repeated. No one connected the dots between your visits or questioned whether the original diagnosis might be wrong.
• You Raised Concerns and Felt Dismissed: You told your GP you were worried and were reassured. However, neither the symptoms nor the anxiety went away. In some cases, you may have been forced to seek a second opinion privately or attend A&E before cancer was finally found.
• Test Results Were Missed/Not Followed Up: Perhaps blood tests showed abnormal results, or a scan flagged something unusual. Despite these concerns, no one acted on it, or the findings were filed without review. By the time the error was spotted, the cancer had moved to a later stage.

What Are the Early Signs of Cancer That GPs Should Spot?

NHS guidelines (known as NICE NG12) set out clear red flag symptoms that should trigger an urgent cancer referral. These are the signs that, when present, a GP is expected to investigate properly. If they were present in your case and were not acted on, that could be significant.

• Unexplained weight loss. Losing weight without trying is a red flag for a number of cancers, including lung, bowel, and pancreatic.
• Blood where it should not be. Blood in stools, urine, or when coughing, even once, should prompt further tests.
• A lump or swelling that does not go away. If any lump, anywhere  on the body, is still there after a few weeks, it needs investigating.
• Persistent symptoms that do not respond to treatment. Such as a cough that antibiotics do not clear, pain that does not ease, and tiredness that does not improve.
• Changes in bowel habits lasting more than three weeks. Going more often, or less often, or finding it harder/easier than normal is one of the known cancer red flags.
• Unexplained anaemia or raised blood markers. These should be picked up on routine blood tests but can be overlooked or coded incorrectly.

Please note: Having one of these symptoms does not mean you have cancer. In most cases, they turn out to be something else entirely. However, the NICE guidelines are clear: these signs must be properly investigated. If they were dismissed without investigation, that is where negligence may have occurred.

Why Does a Missed Cancer Diagnosis Usually Happen?

With cancer, a late diagnosis is rarely caused by one single failure. The NHS Resolution 2025 review found several cancer red flags that were repeatedly missed in general practice. This includes:

Diagnostic overshadowing is when a GP links a new symptom to an existing illness. A new warning sign could be blamed on something already known, prompting no further checks.

Repeat treatment without reassessment was a major theme. Patients received round after round of antibiotics, and no one asked: “Could this be something else?”

Remote consultations featured in more than half of the settled claims. A phone call makes a full examination practically impossible. History-taking was also often rushed.

Fragmented care also played a role. Patients may have seen NHS 111, out-of-hours doctors, and A&E during the early stages of their illness. However, notes from those visits did not always reach the GP, so the full picture was never fully clear to medical teams.

Steps You Can Take if You Think Cancer Red Flags Were Missed

If you or a family member believe that a missed cancer diagnosis caused avoidable harm, there are three clear steps you can take.

1. First, request your medical records. Under UK law, you have the right to see every note, test result, and referral letter from your GP and hospital. These records are the foundation of any negligence investigation.
2. Second, write down what happened. Note the dates you saw your GP, the symptoms you reported, and how you were treated. If a family member was with you at appointments, ask them to do the same.
3. Third, seek specialist legal advice. Medical negligence law is complex. A solicitor who understands cancer misdiagnosis claims will be able to review your records, identify whether the required standard of care fell short, and advise you on whether you have a viable claim; usually at no cost to you for an initial assessment.

It is worth knowing that you generally have three years from the date of the negligence (or from when you became aware of it) to bring a claim. In some cases, this period can be extended, but it is important not to delay.

Common Cancer Misdiagnosis Questions

Q: Is it medical negligence if my GP missed a sign of cancer? It may be. Medical negligence occurs when a healthcare professional fails to meet the standard of care that a competent professional in the same role would provide. If your GP ignored or failed to investigate a red flag symptom that NICE guidelines say should have been referred, that could form the basis of a negligence claim. Each case is assessed on its individual facts.

Q: How long can cancer go undetected before it is too late? There is no single answer — it depends on the type of cancer and how fast it grows. But NHS data is clear: even a four-week delay can affect treatment options and survival. Many cancers are very treatable when caught early. At later stages, options become much more limited. The sooner the diagnosis, the better the outcome.

Q: What if my cancer was eventually diagnosed? Can I still make a claim? Yes. A claim does not require that the cancer was never diagnosed. If there was an avoidable delay — and that delay meant your cancer reached a later stage, required more aggressive treatment, or reduced your chances of recovery — you may still have a valid claim for the harm caused by that delay.

Q: Can I make a claim on behalf of a family member who has passed away? Yes. If a loved one died as a result of a missed or delayed cancer diagnosis, their estate or dependents may be entitled to bring a claim. In the NHS Resolution review, many of the settled claims were brought by families after the patient had already passed away.

Q: How much does it cost to get legal advice on a cancer misdiagnosis claim? An initial assessment with a specialist medical negligence solicitor is typically free and carries no obligation. If your case is taken forward, most firms work on a conditional fee arrangement — meaning you do not pay unless you win. CL Medilaw offers a free, confidential first consultation to help you understand where you stand.

Understand Your Options Following a Cancer Misdiagnosis

A missed or delayed cancer diagnosis can change the course of a person’s life in ways that are impossible to overstate. What often begins as a series of seemingly small decisions: reassurance instead of referral, repeat prescriptions instead of investigation, or test results that were never followed up, can ultimately lead to a diagnosis that comes too late.

Understanding how and why these failures occur is not about assigning blame for the sake of it. It is about recognising when the standard of care may have fallen short, and ensuring that patients and families are not left carrying the consequences alone. Where an earlier diagnosis would likely have led to less invasive treatments, better outcomes, or more time, those questions deserve to be properly examined.

If you believe cancer red flags were missed (or dismissed) during your care, seeking specialist advice can bring clarity at a time when the uncertainty has felt overwhelming. At CL Medilaw, we specialise in complex medical negligence claims, and can help you understand whether what happened to you was avoidable — and what options may now be available. For many clients, that first conversation is less about legal action and more about finally getting answers.

Our experienced team cannot undo what has already happened, but it can provide informed support to help establish accountability. We can help you take a step forward with the knowledge that your experience has been understood and you won’t need to face a delayed cancer diagnosis alone.

Contact us today to talk about what happened and what comes next in a no obligation consultation.