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June, 2025
Case of the Month
Clinical History: A 23-year-old man underwent a CT scan as part of the diagnostic workup following a hockey injury, presenting with dyspnea after the trauma. The scan revealed multiple thoracic nodules localized to the pleura, with the largest measuring 6,4 x 2,7 x 4,4 cm, located at the right lower lobe and extending towards mediastinum. Additional nodules were identified at the diaphragm and middle lobe. The clinical differential diagnosis included paraganglioma, neurofibroma, or possibly CPAM. Due to unsuccessful endoscopic FNAs, thoracoscopic surgery was performed with resection of the largest nodule. Intraoperatively, the nodule presented as a firm tumor measuring approximately 6 cm.
The CT-scan (Figure 1), macroscopic picture (Figure 2), representative histological images (Figures 3-5) and immunohistochemical stains (STAT6) are provided (Figure 6).
Q1. What is the most likely diagnosis?
- Desmoplastic mesothelioma
- Calcifying fibrous tumor of the thorax
- Benign pleural plaque with calcifications
- Nodular amyloidosis
Q2. Which of the following immunohistochemical markers may be positive?
- CD34
- MelanA
- STAT6
- Calretinin
Q3. In which of the differential diagnoses discussed in our case would calcifications be considered uncommon?
- Desmoid fibromatosis
- Benign pleural plaque
- Hyalinized granuloma
- Chronic fibrous pleuritis
Q4. In which age group does this rare entity most commonly occur?
- Children
- Young to middle-aged adults
- Elderly patients
- At any age
Answers to Quiz
Q1. B
Q2. A
Q3. A
Q4. B
Q2. A
Q3. A
Q4. B
Diagnosis
Calcifying fibrous tumor of the thorax
Discussion
Gross examination revealed a well demarcated tumor with a homogenous white cut surface (Figure 2). Histologically, the lesion consisted of dense, keloid-like fibrous tissue with multiple psammomatous microcalcifications and scattered lymphoplasmacytic infiltrates (Figures 3-5). Congo red staining showed no amyloid, IgG4-positive infiltrates were absent, and no TdT-positive lymphocytes were identified. Immunohistochemically, lesional cells were negative for CD34, STAT6 (Figure 6), Pancytokeratin, SMA, Desmin, beta-catenin and S100. Overall, these features were consistent with a calcifying fibrous tumor.
Calcifying fibrous tumor of the thorax is a rare, benign neoplasm, usually presenting as a pleural-based mass. It was first described by Pinkard et al. in 1996. Most patients are asymptomatic, though some may experience local symptoms such as chest pain or dyspnea. It most often occurs in young to middle-aged adults and may appear as solitary or multiple nodules. Similar lesions are found outside the thorax. Malignant transformation or metastasis has not been observed. Whole-exome sequencing studies have identified potential molecular alterations, though these findings are based on limited data and are not currently relevant for routine diagnostics. Surgical resection is the treatment of choice and is generally curative, local recurrence has been described.
According to the current WHO classification 2021, the key diagnostic criteria are based on histomorphology: a paucicellular fibrous mass with calcifications, located in the pleura. The immunohistochemical profile is nonspecific, with only variable CD34 expression.
Immunohistochemistry is useful to exclude the main differential diagnoses, which include, due to the pleural location, solitary fibrous tumor (SFT), desmoid fibromatosis and inflammatory myofibroblastic tumor (IMT). In cases involving the mediastinum, sclerosing mediastinitis may also be considered. The histomorphological features can also mimic amyloidosis or calcified pleural plaques
Calcifying fibrous tumor of the thorax is a rare, benign neoplasm, usually presenting as a pleural-based mass. It was first described by Pinkard et al. in 1996. Most patients are asymptomatic, though some may experience local symptoms such as chest pain or dyspnea. It most often occurs in young to middle-aged adults and may appear as solitary or multiple nodules. Similar lesions are found outside the thorax. Malignant transformation or metastasis has not been observed. Whole-exome sequencing studies have identified potential molecular alterations, though these findings are based on limited data and are not currently relevant for routine diagnostics. Surgical resection is the treatment of choice and is generally curative, local recurrence has been described.
According to the current WHO classification 2021, the key diagnostic criteria are based on histomorphology: a paucicellular fibrous mass with calcifications, located in the pleura. The immunohistochemical profile is nonspecific, with only variable CD34 expression.
Immunohistochemistry is useful to exclude the main differential diagnoses, which include, due to the pleural location, solitary fibrous tumor (SFT), desmoid fibromatosis and inflammatory myofibroblastic tumor (IMT). In cases involving the mediastinum, sclerosing mediastinitis may also be considered. The histomorphological features can also mimic amyloidosis or calcified pleural plaques
Take home message for trainees:
Calcifying fibrous tumor of the thorax is a rare plural lesion. Acellular fibrosis with microcalcifications are key diagnostic features.References
Jia B et al. Multiple calcifying fibrous tumor of the pleura: A case report. Thorac Cancer 2021;12,2271-74.
Mehrad M et al. Whole-exome sequencing identifies unique mutations and copy number losses in calcifying fibrous tumor of the pleura: report of 3 cases and review of the literature. Hum Pathol 2018;78,36-43.
Pinkard NB et al. Calcifying fibrous pseudotumor of pleura. A report of three cases of a newly described entity involving the pleura. Am J Clin Pathol 1996;105,189-94.Contributors
Tereza Losmanova, MD
Staff Pathologist
Institute of Tissue Medicine and Pathology
University of Bern
Bern, Switzerland
Sabina Berezowska, MD
Associate Professor
Institute of Pathology
Lausanne University Hospital and University of Lausanne
Lausanne, Switzerland
Staff Pathologist
Institute of Tissue Medicine and Pathology
University of Bern
Bern, Switzerland
Sabina Berezowska, MD
Associate Professor
Institute of Pathology
Lausanne University Hospital and University of Lausanne
Lausanne, Switzerland
