A mass nearly filling the right side of a woman’s heart has turned out not to be a malignant cardiac tumor, but an exceptionally unusual manifestation of histiocytosis, a group of disorders in which immune-system cells accumulate and form tissue lesions. The case, reported by Chinese researchers in Heliyon, describes a 49-year-old woman whose symptoms and scans initially suggested an aggressive cancer. Only after surgeons opened the right atrium and pathologists examined the tissue did the diagnosis shift toward a rare non-Langerhans cell histiocytosis, possibly related to juvenile xanthogranuloma. The finding highlights how a disease usually associated with skin lesions in children can, in rare circumstances, invade a vital adult organ and mimic a solid tumor.
The patient had experienced intermittent, mild chest tightness for about two weeks, along with visible swelling in her lower legs that became worse after standing for long periods. She had a history of chronic pyelonephritis and hypertension, but her kidney function was generally normal, making renal disease an uncertain explanation for the edema. An echocardiogram revealed an irregular, poorly defined mass measuring approximately 56 by 53 millimeters inside the right atrium. The right atrium receives oxygen-poor blood returning from the body and passes it into the right ventricle, so a lesion of this size could severely disrupt circulation. Computed tomography showed that the mass occupied almost the entire chamber and extended toward the opening of the inferior vena cava, the large vein carrying blood from the lower body to the heart.
The obstruction appeared to explain several of the woman’s clinical problems. The tumor-like tissue interfered with venous return and was associated with pericardial effusion, an accumulation of fluid around the heart, as well as swelling in the legs. Her electrocardiogram also showed a second-degree type II atrioventricular block, a potentially serious disturbance in the electrical signal traveling from the atria to the ventricles. Her ventricular rate was only 46 beats per minute. Although the imaging and the extent of obstruction made malignancy a major concern, the physicians could not safely wait for the mass to declare its nature. They proceeded with surgery after completing the preoperative evaluation, aiming both to relieve the circulatory blockage and to determine what kind of growth had distorted the heart.
The operation revealed a lesion more invasive in appearance than a typical benign mass. The right atrium had lost much of its normal shape and function, while the tissue displayed an infiltrative growth pattern and was hard to separate from surrounding structures. It obstructed blood flow from both the superior and inferior vena cava. Complete removal was not possible, so the surgeons removed as much tissue as they could while focusing on restoring venous circulation. They reconstructed the right atrium using the patient’s own pericardium, the strong membrane surrounding the heart. A sample sent for intraoperative examination produced the first surprise: rather than showing obvious cancer, it contained abundant fibrous tissue within the myocardium, infiltrated by large numbers of inflammatory cells. The result prompted the pathology team to reassess the specimen in detail.
The definitive analysis combined conventional microscopy with immunohistochemistry, a technique that uses antibodies to identify proteins characteristic of particular cell lineages. Tissue was fixed in formalin, embedded in paraffin, sliced into four-micrometer sections and stained with hematoxylin and eosin. Under the microscope, the lesion contained foamy cells and Touton giant cells—multinucleated cells with a distinctive arrangement of nuclei often associated with xanthogranulomatous lesions. The cells showed strong expression of CD163 and Cyclin D1. CD163 is commonly associated with macrophage-lineage cells, while Cyclin D1 can support the interpretation that a population is proliferative rather than merely reacting to nearby injury. Together, the findings suggested an abnormal histiocytic proliferation rather than simple inflammation or scar formation.
Additional stains helped narrow the diagnosis. The lesion showed moderate-to-high staining for BRAF-V600E, a protein alteration linked to activation of the MAPK-ERK signaling pathway in several cancers and histiocytic disorders. However, the staining was not by itself proof that the BRAF gene carried the corresponding mutation, because the team did not perform molecular confirmation using polymerase chain reaction or another genetic assay. The tumor cells were negative for S100, and the report also considered CD1a in evaluating the lesion. S100 and CD1a are characteristic markers used in the diagnosis of Langerhans cell histiocytosis, a different histiocytic disorder. Their absence supported classification as a non-Langerhans cell histiocytosis. On the basis of the Touton giant cells, foamy cytoplasm and immunophenotype, the pathologists favored a lesion resembling juvenile xanthogranuloma, although they acknowledged that the precise subtype could not be established with complete certainty.
Juvenile xanthogranuloma is generally considered a benign proliferative disorder of histiocytes and most often appears as one or more yellowish skin nodules in infants and young children. Its occurrence in adults is less typical, and systemic involvement is rare. In this patient, the heart was the dominant—and apparently extraordinarily extensive—site of disease, with no reported evidence of the classic cutaneous presentation. The investigators therefore used cautious language, describing the mass as a form of histiocytosis and considering both juvenile xanthogranuloma and adult xanthogranuloma possible. They also evaluated Erdheim-Chester disease, another non-Langerhans histiocytosis that can affect the cardiovascular system and is frequently associated with BRAF-V600E alterations. That diagnosis became less likely because imaging showed no symmetrical osteosclerosis of the long bones, a hallmark reported in more than 95 percent of Erdheim-Chester cases, and no retroperitoneal fibrosis or “hairy kidney” appearance.
The patient recovered without major postoperative complications apart from sinus bradycardia. Dynamic electrocardiographic monitoring recorded an average ventricular rate of 54 beats per minute, along with 2,715 atrial premature beats and 39 ventricular premature beats. Because she had no obvious symptoms attributable to the rhythm disturbance, the clinicians did not implant a pacemaker. Her leg swelling improved noticeably after the obstruction was relieved, and the chest tightness disappeared. She was discharged one week after the operation, and follow-up described her as clinically stable. The case nevertheless carries important limitations: the lesion was not completely excised, its histiocytosis subtype remained ambiguous, and the suspected BRAF alteration was not confirmed genetically. Longer follow-up will be needed to determine whether residual disease returns or whether targeted treatment becomes necessary. For now, the report serves as a striking reminder that a mass that looks like a destructive heart cancer can, in rare cases, be an immune-cell disorder—and that tissue diagnosis remains decisive when imaging and clinical appearance point in the wrong direction.
Subject of Research: Rare cardiac involvement by non-Langerhans cell histiocytosis, possibly juvenile xanthogranuloma, in an adult patient
Subject of Research: Biology
Article Title: Cardiac tumor unexpectedly turned out to be a kind of histiocytosis: a case report
Article References: Tao, T., Zheng, J., Ni, Y., Chen, X., & Li, J. (2026). Cardiac tumor unexpectedly turned out to be a kind of histiocytosis: a case report. Heliyon, 12(14), Article e45311. https://doi.org/10.1016/j.heliyon.2026.e45311
Image Credits: AI Generated
DOI: 10.1016/j.heliyon.2026.e45311
Keywords: cardiac tumor, histiocytosis, juvenile xanthogranuloma, non-Langerhans cell histiocytosis, right atrium, BRAF-V600E, cardiac surgery, case report
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SCIENMAG. (August 28, 2026). Unexpected Cardiac Tumor Diagnosed as Histiocytosis in Case Report. https://scienmag.com/unexpected-cardiac-tumor-diagnosed-as-histiocytosis-in-case-report/
SCIENMAG. “Unexpected Cardiac Tumor Diagnosed as Histiocytosis in Case Report.” Scienmag, 28 August 2026, https://scienmag.com/unexpected-cardiac-tumor-diagnosed-as-histiocytosis-in-case-report/. Accessed 28 August 2026.
SCIENMAG. “Unexpected Cardiac Tumor Diagnosed as Histiocytosis in Case Report.” Scienmag. August 28, 2026. https://scienmag.com/unexpected-cardiac-tumor-diagnosed-as-histiocytosis-in-case-report/
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