When Tuberculosis Isn't the Culprit: High-Grade Neuroendocrine Carcinoma as an Elusive Mimicker

Abstract Introduction: High-grade neuroendocrine carcinoma (NEC) of the lung is a rare and aggressive malignancy that may be difficult to distinguish from infections in patients from areas where tuberculosis is endemic. A prolonged productive cough, dyspnea, hemoptysis, weight loss, and recent migration present a diagnostic challenge in immigrant populations with overlapping oncologic and infectious symptoms. Case presentation: A 61-year-old man presented with a worsening cough, dyspnea, and palpitations. He had recently immigrated to the United States and described a productive cough persisting for 16 months while in Bangladesh, with hemoptysis that developed 8-10 months before traveling. The patient had a medical history significant for papillary thyroid cancer, for which he underwent thyroidectomy 18 years ago. Social history was notable for 16 pack-years of smoking. Family history was negative for malignancy. On examination, vitals were unremarkable. BMI was 20.2. He appeared comfortable. He had diminished breath sounds, with absent rhonchi or rales. His heart sounds were regular, without a murmur. His abdomen was soft and nontender, without organomegaly. He had no palpable lymphadenopathy. Laboratory infectious workup was negative. Chest computerized tomography revealed masses in the left upper lobe anterior segment, subcarinal, and bilateral hilar regions, with associated mediastinal lymphadenopathy. Bronchoscopy revealed an obstructive nodule in the bronchus intermedius covered in white mucoid secretions. EBUS demonstrated an enlarged mediastinal lymph node with absent paratracheal or perihilar involvement; biopsies were taken from the abnormal lesions. Immunohistochemical analysis demonstrated markers consistent with neuroendocrine carcinoma, including p40 negativity, SYN positivity, CD56 positivity, Ki-67 >90%, TTF-1 positivity, and CHROM negativity. PET scan was consistent with advanced disease and had an incidental finding of anorectal activity. With concomitant iron deficiency anemia, the patient underwent a negative colonoscopy for masses or metastatic lesions. A brain MRI was negative for metastatic disease. The patient was ultimately treated with a platinum-based chemotherapy regimen with carboplatin and etoposide combined with immunotherapy (atezolizumab) to control the disease. Discussion: This case highlights the diagnostic and management complexities of high-grade NEC in a recent immigrant, with overlapping symptoms initially concerning tuberculosis. Bronchoscopy and immunohistochemistry (SYN+, CD56+, Ki-67 >90%) were pivotal in confirming the diagnosis. Advanced disease required systemic therapy with carboplatin, etoposide, and atezolizumab with a focus on disease control over cure. This case demonstrates the value of multidisciplinary care in navigating through ambiguity.