Progress in Using Circulating Tumor Cell Information to Improve Metastatic Breast Cancer Therapy
Algorithms for incorporating CTC measurements into clinical decision making. (a) Beveridge algorithm  for management of metastatic breast cancer using circulating tumor cell information. (b) An updated algorithm incorporating CTC information in the monitoring strategy. Additional time may be added before a second CTC assessment for patients starting new systemic therapy for CTC counts to stabilize. Declining CTC counts suggest treatment response but require confirmation subsequently. The interval between follow-up CTC counts considers clinical behavior of the tumor. ‡Clinical assessment may include imaging studies, physical examination, histology, CTC enumeration, and serum tumor marker determination. *Disease status may be monitored using CTC counts every 1–3 months, with imaging studies performed if clinical evidence of progression is observed. †Repeat CTC assessment after an additional 1-2 cycles of therapy to verify that CTC counts are <5 per 7.5 mL; CTC counts that remain ≥5 upon retesting suggest treatment failure.