Hello, this is attorney Oh Seung-hyun of Cheongchul Law Firm.

You had annual health check-ups. You had CT scans and endoscopies. You were told, "Everything is normal." But a few months later, another hospital diagnosed you with cancer — already at stage 3 or 4. Later you found that the lesion had already been visible on the very first CT scan. In situations like this, many people ask: "Can I sue the hospital?" Yes, you can. If a lesion was clearly on the images but was missed, if an abnormal finding was discovered but no further testing was advised, or if an oriental-medicine hospital hid another hospital's cancer finding and discouraged surgery — courts have recognized all of these as malpractice. In fact, Korean courts have awarded damages for delayed cancer diagnosis in cases ranging from a misread gallbladder-cancer CT to an ovarian cancer that progressed from stage 1 to stage 4.

Four Types of Malpractice Courts Recognize

(1) CT/Imaging Misreading — It Was on the Image but Missed

The most typical type of malpractice is when a lesion was captured on the imaging but the physician failed to detect it or read it as normal. The Seoul Eastern District Court, in a case where a November 2018 CT showed a lesion in the gallbladder but the medical staff failed to recognize the possibility of malignancy and did not perform further testing, expressly applied the loss-of-chance doctrine and ordered a total of about KRW 42.6 million to be paid to the bereaved family (Seoul Eastern District Court 2020Gadan110138, finalized June 9, 2022). In another case, where a health-screening abdominal CT captured a roughly 1.2–1.4 cm lesion in the head of the pancreas but was read as "no unusual findings," the court found a breach of the duty of care in diagnosis and ordered a total of about KRW 182.82 million to be paid to the bereaved family (Seoul Eastern District Court 2024Gahap106349, May 22, 2025).

(2) Failure to Perform Follow-up Testing + Breach of the Duty to Explain

Discovering an abnormal finding but failing to perform further testing, or failing to inform the patient and refer them to a specialist, constitutes a separate act of malpractice. The Suwon District Court, in a case where the loss of an opportunity for early diagnosis of rectal cancer and the failure to explain a suspected lung-metastasis nodule were both found to be malpractice, ordered payment of KRW 15 million to each plaintiff (Suwon District Court 2024Na72957, February 4, 2026). Notably, this case was a loss for the plaintiff at first instance but was reversed on appeal. Even if you lose at first instance, the judgment on causation can change on appeal, so you should not give up.

(3) Malpractice in Allowing Stage Progression — Ovarian Cancer From Stage 1 to Stage 4

When diagnostic error and failure of follow-up observation overlap, the cancer stage rises sharply. The Incheon District Court found liability for damages, applying the loss-of-chance doctrine, in a case where the medical staff's negligence allowed a stage-1 ovarian cancer to progress to stage 4 without proper diagnosis and treatment (Incheon District Court 2018Gahap62071, June 25, 2019; appeal dismissed and finalized). The difference in the five-year survival rate between stage 1 and stage 4 is several-fold, and this difference forms the basis for calculating damages.

(4) Distorting Another Hospital's Cancer Finding / Strongly Discouraging Surgery

Where a non-oncology facility receives another hospital's report suspecting cancer yet falsely explains to the patient that it is "not cancer but a benign tumor" and strongly urges the patient not to undergo surgery, an independent act of malpractice is established. The Seoul Eastern District Court found malpractice and imposed liability for damages in a case where an oriental-medicine hospital, after directly reviewing another hospital's report (high likelihood of cancer), told the patient "it is not cancer, and you must never choose modern-medicine surgery," thereby delaying treatment for ovarian cancer (Seoul Eastern District Court 2019Gahap109283, May 7, 2020).

When Malpractice Is Denied — When the Doctor Wins

(1) When the Interpretation of Imaging Findings Was Clinically Reasonable

Where the imaging findings do not clearly raise a suspicion of malignancy but fall within the range warranting follow-up observation, malpractice is denied. The Busan District Court denied malpractice in a case where a mammogram showed microcalcifications (BI-RADS 4B) but a subsequent ultrasound showed no abnormal findings and six-month follow-up observation was recommended, holding that "conducting non-invasive follow-up observation for BI-RADS 4A or lower is within a clinically reasonable range" (Busan District Court 2019Gadan343906, November 2, 2021). The mere fact that a biopsy was not performed does not always amount to malpractice.

(2) Short Diagnostic Delay With No Change in Stage

Even if diagnosis was delayed, if the period was short and the stage did not change, loss of chance is denied. The Seoul Southern District Court, in a case where a health-screening misdiagnosis delayed a breast-cancer diagnosis by about one month, held that "the invasive breast cancer was not caused by the defendant medical institution's conduct, and the prognosis after resection of stage 1–2 breast cancer is favorable, so loss of chance is not recognized," excluding treatment costs and lost-income damages and awarding only partial consolation money (Seoul Southern District Court 2022Gadan217975, October 25, 2024). The shorter the delay, the harder it is to prove causation and damages.

(3) Causation — Failure to Prove That Stage Progression Was Caused by the Malpractice

Even if there was a diagnostic delay, if the rebuttal is accepted that the stage progression was due not to the malpractice but to the cancer's own rate of progression or another factor of the patient (such as taking hormone medication), causation is denied. In the above Busan District Court case, the court held that "the possibility of aggravation due to hormone replacement therapy (Cramen tablets) cannot be entirely ruled out, so it is difficult to recognize causation." Clearly identifying, in the medical appraisal, whether the cause of stage progression was medical malpractice is the crux of the litigation.

The Loss-of-Chance Doctrine — How to Legally Argue "If It Had Been Found Earlier"

(1) The Leading Case on the Loss-of-Chance Doctrine

The leading case for the loss-of-chance theory is the Supreme Court's decision in 2012Da117492 (March 12, 2015). In that decision, the Supreme Court held that "if, due to medical malpractice, a patient loses the opportunity to receive timely treatment and there is a substantial likelihood that this affected the treatment outcome, that loss of opportunity can be recognized as a compensable loss." The Seoul Eastern District Court's gallbladder-cancer judgment (2020Gadan110138) expressly cited this Supreme Court decision. The loss-of-chance doctrine treats as the loss not the possibility of a complete cure, but the deprivation of "the opportunity to begin treatment" itself.

(2) Stage Progression = Loss: How Is It Calculated?

Courts compare the stage at which diagnosis would have been possible had there been no delay with the stage actually diagnosed. The difference in five-year survival rates between the two stages, the difference in the intensity of subsequent treatment (broader surgery, added chemotherapy/radiation), and reduced life expectancy form the basis for calculating damages. In the Incheon District Court ovarian-cancer case (2018Gahap62071), the loss of a chance for cure from the rise from stage 1 to stage 4, and even bowel adhesion and bowel necrosis caused by extensive surgery, were recognized as damages. However, when the loss-of-chance doctrine is applied, the plaintiff does not recover the entire loss but only the amount corresponding to the "loss-of-chance ratio," so the award rate often remains at 10–30%.

(3) Loss of Chance in Death Cases — Awards Centered on Consolation Money

When a patient dies due to delayed cancer diagnosis, if a direct causal link with the death cannot be proven, the award is centered on consolation money rather than the entire loss. The Seoul Northern District Court, in a case where a university hospital's diagnostic error and breach of the duty to explain caused the loss of an opportunity for early cancer treatment leading to death, awarded only KRW 10 million in consolation money against a claim of KRW 516 million (Seoul Northern District Court 2023Gahap23153, May 1, 2025). When the case remains at loss of chance and direct liability for the death is not recognized, the award is greatly reduced. For this reason, analyzing causation before litigation is very important.

Key Evidence to Secure

(1) The Original First Images — Secure Them as DICOM Files

The most important evidence in a delayed cancer diagnosis lawsuit is the original DICOM files of the first CT/MRI taken. Screen captures or printouts have low reading precision and are unsuitable for re-reading. Request the original DICOM files together with the reading report in CD or USB form. To prevent the hospital from altering or deleting the images after a dispute arises, you must immediately file for evidence preservation with the court. After securing the original images, having a radiologist at another medical institution re-read them lets you objectively confirm whether there was a reading error.

(2) The Reading Report and Records of Follow-up Measures

How the abnormal finding was recorded in the reading report, and what guidance the attending physician gave the patient after discovering the abnormal finding, are the core issues. You must check whether the medical records contain a "recommendation for further testing" and whether there is a record that the patient refused. A discrepancy between the medical records and the reading report is itself circumstantial evidence of malpractice.

(3) The Re-reading Report From the Later Hospital

Obtaining a report from the hospital that later diagnosed the cancer stating that "the lesion was already present on the earlier images" is powerful evidence. A medical opinion on what stage treatment could have begun at had the first hospital made the diagnosis, and on the difference in five-year survival rates from the current stage, is also key material in litigation.

Practical Checkpoints

• Immediately secure the originals (DICOM files) of previously taken CT/MRI images and the reading reports. Having a radiologist at another medical institution re-read them lets you objectively confirm whether there was a reading error.

• If an abnormal finding was discovered but not disclosed to the patient, or there is no record of a recommendation for further testing, you can assert breach of the duty to inform as a separate act of malpractice. The absence of a recommendation record in the medical records works against the doctor.

• Obtain a report from the hospital that later diagnosed the cancer stating that "the same lesion is confirmed on the earlier images as well." This report is the key evidence for proving a reading error.

• Even if you lose at first instance, do not give up. As in Suwon District Court 2024Na72957, there are cases where the judgment on causation changes on appeal and results in a reversal win. Analyzing the reasoning of the first-instance judgment and redesigning the appellate strategy is important.

• Ask the medical appraisal to clearly specify how the stage changed during the period of diagnostic delay and how much higher the five-year survival rate would have been with early detection. These figures form the basis of the loss-of-chance award.

• If an oriental-medicine hospital or a health-management facility distorted another hospital's cancer-suspicion finding or discouraged surgery, immediately note the time, content, and place where you heard that explanation, and preserve related text messages and call records. This in itself constitutes an independent act of malpractice (Seoul Eastern District Court 2019Gahap109283).

• If death resulted from delayed cancer diagnosis, first confirm with an expert whether a direct causal link between the diagnostic delay and the death can be proven. If causation remains only at "loss of chance," the award may be greatly reduced and centered on consolation money. Predicting the scale of damages before litigation is the starting point for building strategy.

The belief that "they said nothing was wrong at the check-up, so it must be fine" delayed the diagnosis. In the meantime, the cancer went from stage 1 to stage 4, and the chance of a complete cure vanished. If a lesion was on the images but was not read, if a finding was discovered but not disclosed, or if another hospital's report was received but concealed — this is medical malpractice. The very loss of an opportunity for early detection is a legally compensable loss.