Volume Doubling Time of Pulmonary Carcinoid Tumors Measured by Computed Tomography

Pulmonary carcinoid tumor (PCT) is a slow-growing lung neoplasm, however the true growth rate of this cancer is unknown. In a series of 18 PCTs we find that typical and atypical pulmonary carcinoids have median volume doubling times of 977 days and 327 days, respectively. Clinicians should appreciate the remarkably slow growth of typical PCT when managing solitary pulmonary nodules. Introduction: Pulmonary carcinoid tumor (PCT) is a rare neuroendocrine lung neoplasm comprising approximately 2% of lung cancer diagnoses. It is classified as either localized low-grade (typical) or intermediate-grade (atypical) subtypes. PCT is known clinically to be a slow-growing cancer, however few studies have established its true growth rate when followed over time by computed tomography (CT). Therefore, we sought to determine the volume doubling time for PCTs as visualized on CT imaging. Materials and Methods: We conducted a retrospective analysis of all PCTs treated at our institution between 2006 and 2020. Nodule dimensions were measured using a Picture Archiving and Communication System or retrieved from radiology reports. Volume doubling time was calculated using the Schwartz formula for PCTs followed by successive CT scans during radiographic surveillance. Consistent with Fleischner Society guidelines, tumors were considered to have demonstrated definitive growth by CT only when the interval change in tumor diameter was greater than or equal to 2 mm. Results: The median volume doubling time of 13 typical PCTs was 977 days, or 2.7 years. Five atypical PCTs were followed longitudinally, with a median doubling time of 327 days, or 0.9 years. Conclusions: Typical pulmonary carcinoid features a remarkably slow growth rate as compared to more common lung cancers. Our analysis of atypical pulmonary carcinoid included too few cases to offer definitive conclusions. It is conceivable that clinicians following current nodule surveillance guidelines may mistake incidentally detected typical carcinoids for benign non-growing lesions when followed for less than 2 years in low-risk patients.

Automated summary

Pulmonary carcinoid tumor is a slow-growing lung neoplasm, with typical carcinoids showing remarkably slow growth. Clinicians may mistake typical carcinoids for benign non-growing lesions if followed for less than 2 years.