How Cognitive Bias Nearly Hid a Teenager’s Cancer Behind a Benign Diagnosis

A seventeen-year-old boy from rural Montana arrived at a vascular anomalies center with what seemed like a textbook case. A multi-cystic mass in his lower left neck had been diagnosed clinically and radiographically as a macrocystic lymphatic malformation, a congenital anomaly of the lymphatic system that is often managed with aspiration and sclerotherapy. The imaging was convincing, the referral pathway was standard, and the initial plan followed established practice. Yet the true diagnosis turned out to be something far more dangerous: a massive mixed germ cell tumor, roughly 98 percent of it an immature teratoma, wrapped around the aorta, the inferior vena cava, his kidneys, ureters, and iliac vessels. A new case report from Children’s Hospital Colorado, published in Frontiers in Cancer Control and Society, dissects how anchoring and confirmation bias nearly cost precious time, and how a structured, multidisciplinary re-evaluation ultimately saved the patient’s life.

The story began when the teenager developed a progressively enlarging neck mass causing discomfort and airway compression. Magnetic resonance imaging showed a left lower neck multi-cystic lesion extending into the supraclavicular region and down into the mediastinum, findings read as consistent with a macrocystic lymphatic malformation. Local otolaryngologists attempted aspiration but obtained insufficient fluid to relieve the compression, prompting transfer out of state for specialized care at a vascular anomaly center. His past medical, family, and psychosocial history offered no red flags, with no known genetic syndromes and no prior malignancy. On the surface, everything pointed toward a benign vascular anomaly.

At the specialty center, evaluation confirmed left cervical cystic masses, the largest measuring seven by seven centimeters. The lesion was non-tender but firm, a detail that raised concern for intralesional hemorrhage. Then came the first cracks in the diagnostic narrative. Additional history revealed a forty-pound weight loss, vomiting, and early satiety over the preceding months, symptoms that are distinctly atypical for an isolated lymphatic malformation. On examination, the boy’s abdomen was markedly distended with a palpable mass spanning the left upper and lower quadrants. Full-body MRI and magnetic resonance angiography revealed a large multiloculated cystic abdominal mass, initially interpreted as additional sites of lymphatic malformation. The differential diagnosis included complex lymphatic anomaly, venous-lymphatic malformation, and germ cell tumor, with evolving findings progressively arguing against a vascular cause.

Interventional radiology was consulted for aspiration and possible sclerotherapy, the standard treatment for macrocystic lymphatic malformations. What the procedures yielded should have been a turning point. The abdominal fluid was brown-tinged and the cervical fluid was clear, both appearances atypical for lymph or chyle, the milky lymphatic fluid expected from a true lymphatic lesion. Sclerotherapy was attempted on the cervical lesion, but fluid analysis told a different story: a triglyceride level of just 13 milligrams per deciliter and a lymphocyte fraction of only 2 percent, values wholly inconsistent with lymphatic fluid. Further sclerotherapy attempts were discontinued. The treatment was failing not because the technique was flawed, but because the underlying diagnosis was wrong.

Multidisciplinary consensus led to surgical resection of the abdominal mass, a twelve-hour operation that removed 95 percent of a retroperitoneal tumor measuring 25 by 25 by 20 centimeters. The mass had both solid and cystic components and encased critical structures, including the aorta, inferior vena cava, kidneys, ureters, and iliac vessels. Pathology revealed a mixed germ cell tumor, approximately 98 percent immature teratoma, with additional mature teratomatous elements including squamous, neural, and gastrointestinal-type epithelium. Foci of embryonal carcinoma and areas consistent with yolk sac tumor were also identified. Tumor markers confirmed the diagnosis: alpha-fetoprotein was 1,240 nanograms per milliliter against a reference range of zero to eight, and human chorionic gonadotropin was 268 milli-international units per milliliter against a reference of zero to five. Following pathologic confirmation, the patient transitioned to oncology care and began standard bleomycin, etoposide, and cisplatin chemotherapy without dose modification or delay. Follow-up imaging showed regression of residual disease, tumor markers declined appropriately, and treatment was well tolerated without significant toxicity or interruptions.

The authors of the report argue that this case is a vivid illustration of diagnostic anchoring, the cognitive tendency to rely too heavily on initial information and interpret everything that follows in relation to that first reference point. Once the lymphatic malformation label was attached, subsequent findings were filtered through that lens. Confirmation bias compounded the problem: clinicians sought and favored information that supported the existing hypothesis while downplaying evidence that contradicted it. The firm texture of the mass, the systemic symptoms, the multifocal disease across non-contiguous anatomic compartments, the atypical aspirate characteristics, and the failure to respond to sclerotherapy were all signals that something did not fit. Each was initially absorbed into the vascular anomaly framework rather than triggering a fundamental reconsideration.

The report lays out explicit diagnostic checkpoints that should prompt clinicians to question a lymphatic malformation diagnosis. These include systemic symptoms such as weight loss or early satiety, which are atypical for isolated lymphatic disease; multifocal involvement across separate anatomic compartments; aspirate characteristics inconsistent with chyle or lymph; and lack of biochemical or clinical response to sclerotherapy. When an initial diagnosis fails to account for the full clinical picture, the authors contend, structured re-evaluation is essential to avoid diagnostic delay. In this case, the presence of gastrointestinal symptoms and dramatic weight loss deviated from the typical lymphatic malformation course, yet an atypical complex vascular anomaly with possible intestinal lymphangiectasia was initially considered before the team pivoted toward malignancy.

The stakes of such cognitive errors are far from abstract. Diagnostic errors account for approximately 75 percent of malpractice lawsuits and 38 percent of total payouts, and pediatricians report diagnostic errors affecting patient outcomes at least annually. Misdiagnosis remains a leading cause of avoidable harm and cost in medicine. Lymphatic malformations are typically diagnosed through history, examination, and imaging, but their radiologic features can be nonspecific and can be confused with teratomas, particularly when cystic morphology is interpreted without integrating systemic symptoms or treatment response. A limited number of prior reports describe teratomas mimicking vascular anomalies, but few address the diagnostic delay caused specifically by cognitive bias. Unlike cases diagnosed early through surgery, this case shows how diagnostic mimicry and specialty silos can delay recognition when no one actively re-evaluates the working diagnosis.

The authors emphasize that overcoming bias requires deliberate tools rather than good intentions alone. Metacognition, the practice of actively reflecting on one’s own clinical reasoning, allows clinicians to recognize when their thought processes may be drifting toward premature closure. Cognitive forcing strategies offer structured ways to break out of entrenched thinking: case-based discussions with peers, red team reviews inviting external expert critique, prospective hindsight that imagines future outcomes to anticipate pitfalls, the five whys technique for root-cause analysis, decision trees and flowcharts, deliberate consideration of contrary evidence, and simulation-based reviews. Clinicians should also avoid the pseudo-diagnostic effect, in which irrelevant data are used to shore up a diagnosis. The report suggests two questions worth asking whenever a diagnosis fails to explain the clinical course: What else could this be? And what doesn’t fit?

Ultimately, the case is a story of both failure and rescue. The initial reliance on typical referral pathways without questioning atypical features delayed definitive treatment, a limitation the authors acknowledge candidly. But clinical intuition, combined with a structured multidisciplinary approach drawing on radiology, interventional radiology, pediatric surgery, pathology, and oncology, broke through the anchoring. The authors argue that balancing intuitive and analytical thinking, while remaining vigilant for bias, is central to diagnostic excellence, and that medical education should emphasize debiasing strategies, guided reflection, and structured re-evaluation. Time pressures, sleep deprivation, and cognitive overload all work against consistent analytical reasoning, which is why they also point to technology such as clinical decision support systems and artificial intelligence tools as potential safeguards. Improving the diagnostic process, they conclude, is both a clinical and a moral imperative, and recognizing diagnostic mimicry while applying critical thinking throughout the clinical course can improve care in complex pediatric conditions such as mixed germ cell tumors and lymphatic malformations.

Subject of Research: Cognitive bias and diagnostic error in the diagnosis of a pediatric mixed germ cell tumor mimicking a lymphatic malformation

Article Title: Case Report: When bias clouds judgment in diagnosing a pediatric mixed germ cell tumor

Article References: Elsabbagh, E. M., Maloney, L., Kulungowski, A., Annam, A., Siegele, B., & Nakano, T. A. (2026). Case Report: When bias clouds judgment in diagnosing a pediatric mixed germ cell tumor. Frontiers in Cancer Control and Society, 4, Article 1638457. https://doi.org/10.3389/fcacs.2026.1638457

Image Credits: AI Generated

DOI: 10.3389/fcacs.2026.1638457

Keywords: cognitive bias, diagnostic error, anchoring bias, confirmation bias, pediatric germ cell tumor, immature teratoma, lymphatic malformation, diagnostic mimicry, interventional radiology, metacognition, pediatric oncology, multidisciplinary diagnosis