A 32-year-old man with a medical history significant for cigarette smoking (10 pack years) presented to the emergency department with chest pain that started several months earlier. The pain was initially localized to the left anterior region of the chest and later began to involve the left shoulder with radiation to the left arm. No apparent motor or sensory deficits in the left upper extremity were found, and no detectable elements of Horner syndrome were observed. 

A subtle left apical opacity was noted on single-view anteroposterior chest radiograph (Figure 1), and a non–contrast-enhanced chest radiograph (Figure 2) disclosed a 4.0×4.0×2.7-cm lesion in the left medial pulmonary apex, abutting the superior mediastinum. A focus of air was seen within the periphery of this lesion, along the lateral inferior aspect. The lesion demonstrated a mildly spiculated border, suspicious for malignancy. 

The patient was admitted to the hospital for further evaluation. Staging imaging studies included computed tomography (CT) of the head, CT of the abdomen and pelvis, positron-emission tomography of the chest, magnetic resonance (MR) imaging of the brain, and MR imaging of the thoracic outlet. No evidence of other primary lesions, nodal involvement, direct brachial plexus involvement, or metastases was found. 

Computed tomography-guided core-needle biopsy was performed, and tumor cells were noted to have the histopathologic appearance of signet ring cells. Immunohistochemical staining yielded a profile consistent with primary lung SRCC, including TTF-1 positivity, CK7 positivity, napsin A positivity, CDX-2 negativity, and CK20 negativity. The result of PD-L1 analysis was also positive for primary lung SRCC. Fluorescence in situ hybridization panel testing did not show evidence of rearrangements of the ALK or ROS1 genes. Stage IIb T3N0 primary lung SRCC was diagnosed. 

The patient was treated with chemotherapy (etoposide and cisplatin), surgical resection, radiation, and immunotherapy with pembrolizumab. He developed adrenal and brain metastases approximately 13 months after initial diagnosis and received 2 courses of gamma stereotactic radiosurgery, whole brain radiotherapy, and additional chemotherapy. His disease eventually progressed, and he was provided hospice care after leptomeningeal involvement developed. He died approximately 21 months after the initial diagnosis. 

Given the rarity of primary lung SRCC, any reported case presents an opportunity to enhance our understanding of the disease. Several features of this case are atypical. First, our search of the literature revealed that our patient was the youngest documented patient with primary lung SRCC in a male ever-smoker. Second, primary SRCC is strongly associated with a solid tumor type.³ A review of the literature did not reveal any known cases of cavitary primary SRCC. Third, less than 5% of all lung cancers are Pancoast tumors. Of that 5%, about two-thirds are adenocarcinomas, with the remainder being large cell and squamous cell carcinomas.¹¹ A search of the literature revealed no other reported cases of primary SRCC presenting as a Pancoast tumor. Last, this patient's 21-month survival was uncharacteristically long.⁸ These atypical demographic, anatomic, and prognostic features suggest potentially greater variability in the assumed typical behavior of primary lung SRCC. Conversely, the immunohistochemical staining profile of this case was quite typical, reinforcing the reliability of these markers in diagnosing primary lung SRCC. 

Although this case involves a disease that most physicians will never encounter, it illustrates several points that are applicable to the everyday practice of medicine. A careful history performed in the emergency department alerted the physician to the possibility of a superior sulcus mass and facilitated the recognition of subtle findings on the chest radiograph. In this age of increased technology use, the value of basic clinical skills can sometimes be underappreciated. This case serves as a reminder of the diagnostic power of a thorough history. Simultaneously, it also provides an example of the utility of technologically advanced diagnostic techniques. The need to separate true SRCC from histopathologic mimics and primary lung SRCC from metastatic SRCC necessitates the use of immunohistochemical staining. An accurate diagnosis of primary lung SRCC in this patient could not have occurred without it. 

This case report illustrates that primary lung SRCC, a rare disease itself, can present in an atypical fashion and in an atypical patient demographic. Specifically, it demonstrates that primary lung SRCC can occur in young ever-smokers and, furthermore, that it can cavitate and present as a Pancoast tumor. Additional case reports, case series, and large studies are necessary to refine our understanding of the characteristics of primary lung SRCC, the prognostic significance of these characteristics, and the selection of specific therapies based on the presence or absence of gene rearrangements.