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Pulmonary carcinoid tumor (PCT) is a rare neuroendocrine lung cancer that is known clinically to be a slow-growing neoplasm. Few studies have established the true growth rate of these tumors when followed over time by radiography. Therefore, we sought to determine PCT tumor doubling time using longitudinal Computed Tomography (CT) scans. Nodule guidelines may misclassify early PCT nodules with a small diameter as benign if tumor growth is too slow to be appreciable on follow up radiographic scans completed between six months and two years after initial detection.


We performed a retrospective analysis of available CT imaging of all PCTs treated at Thomas Jefferson University Hospital between 2006-2020 where radiographic follow up occurred prior to biopsy or resection. Nodule dimensions were measured manually using Phillips Intellispace PACS or retrieved from radiology reports. Tumor doubling time was calculated for all tumors demonstrating definitive growth (an increase in average diameter ≥ 2 mm) over a follow up interval of at least two years.


Fifteen patients had pathologically proven PCT with pre-resection observation times exceeding two years. 12/15 (80%) were typical carcinoids and 3/15 were atypical. 11/12 of the typical PCTs demonstrated definitive growth with a median doubling time of 140 weeks (mean = 161 ± 105 weeks).


The median doubling time of typical PCT was 141 weeks, or almost three years. It is conceivable that PCTs detected early with small diameter may be mistaken for benign non-growing lesions when followed for less than two years in low-risk patients.