Herein, we demonstrated that a CTC isolation system that targets mHsp70 on tumor cells [27] is superior to an EpCAM mAb-based system since at least equal, but mostly higher numbers of CTCs could be isolated from the peripheral blood of patients with metastatic prostate cancer who received a [177Lu]-PSMA-radioligand therapy later on [49], endometrial carcinoma [50], lung and squamous cell carcinoma of the head and neck. Here, FOLH1 is linked to squamous cell carcinoma.