The ‘Starburst’ Sign: A Novel Description of PET Images in Carcinoma of Unknown Primary

Discussion

CUP is a complex disease with not fully understood underlying pathophysiology. Three hypothetical scenarios have been suggested: a cancer may develop without a premalignant lesion or primary cancer; or a very early primary cancer develops that quickly metastasises, or that chromosomal instability may play a role in the aggressive presentation of metastatic disease leading to subsequent chemoresistance (4). Providing patients and trainee physicians with a simple description of this process would help them to understand their disease and the subsequent assessment and treatment process.

When a star reaches the end of its life cycle, the depletion of its core fuel initiates a sequence of events leading to its contraction and collapse due to gravitational forces. This process typically unfolds in two distinct phases. Initially, the inner core undergoes a reduction in size, followed by the inward compression of the outer core, resulting in its ultimate collapse. As a consequence of this cataclysmic event, an intense release of energy and matter occurs, manifesting in an explosive phenomenon (5). Given the striking resemblance of the observed PET scan appearance (where no primary is identifiable, but high-volume metastatic disease is present) to this celestial occurrence, the lead author aptly coined it the ‘Starburst’ sign. In this analogy, the primary tumour assumes the role of a dying star, wherein its physical remnants are diminished, and only the radiant burst-like elements of the star persist, mirroring the metastatic burden evident in PET scans. This metaphorical description encapsulates the essence of the observed radiological presentation, contributing to a deeper understanding of the pathophysiology and implications of the identified metastatic lesions.