Reasons are that it is regarded as too invasive and
no validated methods are available to reliably enumerate
disseminated tumor cells routinely in clinical laboratories.
Detection of tumor cells in the blood is an
attractive alternative as a validated method is available
and the presence of CTC in breast cancer patients with
metastatic disease has shown to be an independent
prognostic factor for progression-free and overall survival
[22,28,29]. The frequency of CTC is, however, low
and only 52% of patients starting first-line chemotherapy
have 5 or more CTC in 7.5 ml of blood [23]. In
patients prior to pre-neoadjuvant chemotherapy and
definitive surgery the frequency is even lower and 1 or
more CTC were detected in 7.5 ml of blood in 23 to
24% of these patients [29,33]. In the ongoing German
SUCCESS study, 21% of patients at primary diagnosis
of breast cancer, 1 or more CTC were detected in 23
ml of blood [34,35]. In this study, four 7.5 ml aliquots
of blood from four blood collection tubes were investigated
for the presence of CTC to increase the sensitivity
of CTC detection with the FDA-cleared CellSearch
CTC test.