RB1 and neoplasm: We concluded that, despite the large number of studies, relatively few liquid biopsy markers have been studied in sufficient depth and with sufficiently consistent results: nonspecific markers, such as circulating tumor DNA fraction, circulating tumor cell count, as well as androgen receptor splice variant 7 and androgen receptor overexpression and amplification, and potentially also three tumor suppressor genes, namely, PTEN, RB1, and TP53.