The association between tuberculosis (TB) and oncological processes is complex and continues to be significant due to various factors, including the recent increase in the prevalence of both diseases. Diagnostic difficulties arise due to similarities in clinical and radiological findings between TB and tumor processes in the respiratory system, leading to frequent diagnostic errors.¹

Tuberculous pleurisy (TP) or fluid accumulation on one side of the pleura caused by TB outside the lungs commonly affects young people with strong immune systems and presents with symptoms such as breathing difficulty, fever, cough, sharp chest pain, nocturnal sweating, weight loss, and general discomfort.^2,3

Diagnosis can be challenging due to the low sensitivity of microbiological tests on pleural fluid, such as direct examination and cultures, which typically ranges from 10-30%.⁴ Biomarkers, such as pleural adenosine deaminase and polymerase chain reaction, can help diagnose Mycobacterium (M.) TB infection,⁵ as can the Mantoux test and interferon gamma release assays, such as QuantiFERON-TB Gold.^6-8 However, a pleural biopsy obtained through medical thoracoscopy or a transthoracic route is the most reliable method for diagnosing M. TB infection, as it directly isolates bacteria and demonstrates the presence of caseating granulomas. Despite being the preferred diagnostic method, this approach is highly invasive and has a significant number of documented cases in the literature where the results are falsely negative, ranging from 15-20%.⁹

In this case report, we describe the occurrence of TP in a patient with a history of malignancy and the challenges in diagnosing this condition. A patient with a history of breast cancer (BC) and TP received a combination anticancer treatment at our hospital. The patient underwent routine clinical, radiological, laboratory, and instrumental examinations, including parietal pleural puncture biopsy, as well as microbiological and immunological tests.

Previous studies have provided substantial evidence supporting the co-occurrence of cancer and pulmonary TB.^9-13 Patients with cancer who undergo radiation and chemotherapy may have compromised immune systems, making them more susceptible to contracting TB.¹⁴ However, there is a lack of detailed information regarding this phenomenon, and the current research has not provided a comprehensive understanding of the association between BC and TP.

Diagnosing TP in patients with cancer is complicated by the nonspecific symptoms exhibited by clinical, laboratory, and radiological tests, as well as the absence of M. TB in sputum. TP must be considered when a patient presents with fresh pleural effusion. Overlooking this can lead to pulmonary or extrapulmonary TB.¹⁵ To accurately diagnose pleural effusion in patients with cancer, physicians must employ various diagnostic techniques, including morphological and microbiological confirmation, and seek specialist consultation.

Malignant tumors, dull chest pain, large pleural effusion, blood-contaminated pleural effusion, and abnormal chest radiograph shadowing strongly indicate malignant pleural effusion, whereas a temperature of 37 °C or higher and recent illness within 30 days decrease the probability. Irregular silhouettes on chest CT scans have demonstrated high sensitivity and specificity.^16,17 Pleural fluid tumor markers, such as carcino-embryonic antigen (threshold of 5ng/mL) with 98.6% accuracy and cancer antigen 19-9 (cutoff of 100 ng/mL) with 100% specificity, are diagnostically valuable. However, their positivity rate of approximately 70% makes them unreliable for excluding malignant tumors. Pleural effusion cytology has a diagnostic accuracy of 75%, suggesting limited sensitivity.¹⁸

TP may resolve without intervention; however, it can later lead to the development of active TB.¹⁹ A diagnosis of TP cannot be solely based on the resolution of pleural effusion with anti-TB medication. A mycobacterial culture of sputum is recommended for diagnosing suspected TP.^20,21 In our case, the patient had characteristic Langhans giant cells on histological examination, consistent with previous research involving a larger number of cases.²²

Diagnosing the cause of TB can be difficult, particularly when attempting to differentiate between TP and BC. The clinical, laboratory, and radiological signs of tuberculous pleurisy are not sufficiently specific, and microbiological methods are rarely used to verify diagnosis. In some cases, the absence of TB in sputum may be due to isolated pleural lesions without lung tissue involvement. TB is also rarely found in pleural exudates due to dilution and can only be detected in very rare cases by culture or microscopy. Given the uncertainty of examination data in hospitals, it is essential to develop personalized diagnostic strategies for pleural effusions in oncological patients. An accurate diagnosis and treatment plan requires a comprehensive range of diagnostic methods, including morphological and microbiological verification and consultation with a physician.

Although no diagnostic test methods use chest computed tomography in detecting carcinomatous pleurisy, repeated pleural effusion cytology is crucial to exclude this condition, even after initiating anti-TB treatment. Furthermore, pleural biopsy is a valuable diagnostic tool for identifying malignant pleural effusion and TB.

In this case, radiography also identified fluid in the left pleural cavity with lung parenchymal involvement, supporting the use of sputum culture for diagnosing TP. Therefore, using both effusion and sputum cultures is a rational approach for diagnosing TP that can provide accurate diagnostic results.

Physicians must employ a combination of diagnostic techniques, including morphological and microbiological confirmation, to accurately diagnose pleural effusion in this patient population. The co-occurrence of cancer and TB is supported by previous studies, and patients with compromised immune systems due to cancer treatment may be more susceptible to TB. Prompt diagnosis and treatment of TP are crucial to prevent the development of active TB.

The patient signed an informed consent for the presentation of details of her disease in this journal.