Aim: We sought to examine the significance and utility of serial serum CA15-3 levels in assessing disease progression in patients with MBC receiving systemic therapy.
Methods: We reviewed records of consecutive MBC patients treated between 01/01/2012 & 30/08/2016 in SWSLHD to identify those with at least three serial serum CA15-3 levels and one progress imaging study during systemic therapy. The serial percentage change in CA15-3 was calculated and each significant rise in CA15-3 was compared with corresponding radiological or clinical evidence of progression. Disease biology and sites of disease were also examined.
Results: From 141 eligible patients there were 2217 occasions of measured CA15-3 levels. Overall, the median CA15-3 level was 40ku/L (range 3-22320). CA15-3 levels varied according to HER2/ER as follows: HER2+ve (median 28ku/L, range 6-3674), HER2-ve (48ku/L, range 3-22320), ER+ve (45ku/L, range 3-22320), ER-ve (28ku/L, range 6-2188) and triple negative (median 20ku/L, range 6-536). Median CA15-3 levels also varied according to metastatic site. In 1469 instances where the CA15-3 rise was less than 20%, there was no radiological evidence of disease progression (negative predictive value= 83%). In 151 instances, CA15-3 levels increased by 20% or more and corresponded with progression (positive predictive value = 34%). In 1672 instances where the CA15-3 level increased by less than 50%, there was no demonstrated disease progression (negative predictive value = 81%) and in 77 cases of CA15-3 increases of greater than 50% there was demonstrated disease progression (positive predictive value 47%). For 20% increase in CA15-3, the sensitivity was 33% and specificity 83% and for increase of 50%, sensitivity was 17% and specificity was 95%.
Conclusion: Our study suggests that CA15-3 increases of greater than 50% may be more useful than lower thresholds for assessing disease progression during systemic therapy for MBC. Prospective studies are required to further test this threshold.