Primary adenoid cystic carcinoma (ACC) of the lung is an extremely rare tumor, accounting for only 0.04-0.2% of all lung cancers. Characterized by slow progression, a propensity for recurrence and relapse, and often presenting with subtle symptoms, it poses significant diagnostic and therapeutic challenges. This case study presents a unique radiological presentation of a primary ACC of the lung in a 50-year-old male patient, aiming to highlight the diagnostic difficulties and treatment strategies for this rare and challenging malignancy. The patient's extensive disease highlights the need for increased awareness among clinicians about this unusual presentation and the complexities in management of such cases.

Primary pulmonary adenoid cystic carcinoma (ACC), though rare, has been documented in various locations beyond the lung, including salivary glands, nose, sinuses, and other organs. While a slight female predominance exists, there are no definitive risk factors identified, although smoking may be a protective factor. Common respiratory symptoms include dyspnea, cough, and chest pain. Existing literature lacks case reports detailing lesions of the size presented in this case study. Histological subtypes include cribriform, tubular, and solid, with the solid type associated with a poorer prognosis. Differentiating ACC from other lung tumors like carcinoid tumors or adenocarcinomas often requires immunohistochemistry, utilizing markers like TTF1, CD56, and chromogranin. The effectiveness of targeted therapy remains limited, with studies reporting a lack of common mutations. Surgical resection is the gold standard treatment, but its feasibility depends on tumor size and extent. Radiotherapy's role is less well-defined, often reserved for incomplete resections or unresectable disease. Prognosis is heavily influenced by histological type, TNM staging, and the success of surgical removal.

A 50-year-old male farmer, with a 30-pack-year smoking history but no history of tuberculosis or family cancer history, presented with a four-month history of dry cough and dyspnea. Physical examination revealed dullness on percussion and diminished breath sounds in the left lower lung field. Chest radiography showed an opaque left hemithorax with mediastinal shift. Computed tomography (CT) of the chest revealed a large cystic mass occupying the entire left hemithorax. Hydatid serology was negative. Bronchoscopy revealed an endobronchial mass occluding the left upper lobe bronchus. A biopsy confirmed the diagnosis of adenoid cystic carcinoma exhibiting a cribriform pattern with characteristic tumor cells surrounding pseudoglandular cavities containing mucoid material. Immunohistochemistry was negative for thyroid transcription factor 1 (TTF1). Cervicofacial MRI excluded salivary gland metastasis. PET and brain scans revealed a large solid cystic left pulmonary mass, mediastinal lymphadenopathy, and hypermetabolic micronodules in the right upper lobe, resulting in a T4N3M1a classification (8th edition TNM). Given the stage IVa diagnosis, palliative chemotherapy was administered. After three cycles of chemotherapy and eight months of follow-up, the patient's condition deteriorated (PS 3), though thoracic CT showed a significant reduction in the lung mass.

This case presents a unique instance of a large primary adenoid cystic carcinoma of the lung, exhibiting an exceptionally large size and distinct radiological presentation, which has not been previously reported in the literature. The tumor occupied the entire left hemithorax, creating a substantial diagnostic challenge due to its unusual size and appearance. Histopathological examination and immunohistochemistry confirmed the diagnosis, with the absence of TTF1 expression supporting the primary origin of the ACC within the lung. The patient's T4N3M1a staging at diagnosis indicated an advanced disease state, prompting palliative chemotherapy as the most appropriate treatment approach. The response to chemotherapy, resulting in a significant reduction of the tumor size, was observed. The patient's clinical course and response to treatment underscore the significant challenges involved in managing advanced stages of this rare lung cancer type.

This case highlights the significant challenges posed by the diagnosis and treatment of primary pulmonary ACC, especially when presented with the unusual features reported here. The atypical radiological presentation, large tumor burden, and aggressive progression demonstrated by the patient underscore the need for greater vigilance and more detailed diagnostic workup for such cases. The absence of response to standard treatment approaches for lung cancers highlights the importance of further research into tailored therapies for pulmonary adenoid cystic carcinoma. This unusual presentation should alert clinicians to consider ACC as a differential diagnosis in such circumstances, despite its rarity. Given the patient's advanced stage at diagnosis, palliative treatment was implemented, highlighting the limitations in current management strategies for this tumor type.

This case report underscores the significant diagnostic and therapeutic challenges posed by primary adenoid cystic carcinoma of the lung, particularly when it presents with an unusually large size and complex radiological findings. The case emphasizes the importance of a high index of suspicion and thorough investigation, including immunohistochemistry, to establish a correct diagnosis. Further research into more effective treatment strategies for advanced-stage pulmonary ACC is necessary to improve patient outcomes. This report is compliant with SCARE 2020 guidelines.

This study presents a single case report, limiting the generalizability of the findings to a wider population. The retrospective nature of the data collection may introduce potential biases. The limited follow-up period after the initial diagnosis prevents a complete assessment of long-term survival and treatment outcomes.