Situs inversus totalis and lung cancer: a case report of surgical resection after neoadjuvant chemoimmunotherapy for stage IIIB squamous cell carcinoma

Immune checkpoint inhibitors (ICIs) have emerged as a promising therapeutic strategy for lung cancer. This case report describes a patient with situs inversus totalis (SIT) and initially unresectable, advanced lung squamous cell carcinoma (LSCC) who successfully underwent surgical resection following neoadjuvant therapy with pembrolizumab and chemotherapy. The patient was incidentally found to have SIT and a 6.5 × 5.0 cm mass in the right upper lobe (RUL) with hilar and mediastinal lymphadenopathy on a local chest CT scan. PET-CT scan revealed the RUL lesion (approximately 6.6 cm, SUVmax 13.7) and multiple hypermetabolic lymph nodes in the right hilum and station 4R (largest 1.8×1.8 cm, SUVmax 2.5-5.2). EBUS/TBNA was not performed due to limited availability at the initial treating institution. The tumor was deemed unresectable due to its large size (6.6 cm), central location involving the apical segment bronchus, and bulky N2 disease (station 4R, >2 cm), which increased the risk of incomplete resection and recurrence. A CT-guided biopsy confirmed squamous cell carcinoma. The patient was staged as cT3N2M0 (stage IIIB) and received three cycles of neoadjuvant pembrolizumab (200 mg), cisplatin (60 mg), and paclitaxel (270 mg). A repeat PET-CT at our institution showed significant reduction of the tumor (approximately 1.9×1.7 cm, SUVmax 8.9) and mediastinal (stations 3A, 4) and hilar lymph nodes with decreased metabolic activity (SUVmax 2.5). The restaging was ycT1cN1M0 (stage IIA). Following a multidisciplinary team (MDT) discussion, the patient underwent video-assisted thoracoscopic surgery (VATS) right upper lobectomy with mediastinal lymph node dissection. The final pathology confirmed a pathological complete response in the lymph nodes and minimal residual disease in the primary lesion, yielding a postoperative pathological stage of ypT1cN0M0 (stage IA3). Postoperative management included supportive care, infection control, and airway clearance. The patient was discharged on postoperative day 4 and subsequently received adjuvant pembrolizumab monotherapy. This case demonstrates that neoadjuvant chemoimmunotherapy can effectively downstage initially unresectable advanced LSCC, even in a patient with SIT, creating an opportunity for successful surgical intervention and potentially improving outcomes, thereby informing future clinical practice.