There are multiple definitions:

1. cluster determinant, where x is a number assigned by antigen classification(English)

   • numbers run from 1 through 247 or even higher, e.g. CD10=CALLA
   • Classification

2. CTC [circulating tumor cell] Derived explant(English)

   • liquid biopsy provides important information through the analysis of circulating tumor cells (CTCs), and circulating tumor-derived material like circulating tumor DNA
   • CTC, ctDNA
   • Biopsy, Oncology
   • https://doi.org…cer.2022.03.013