Efficacy of Lapatinib in Therapy-Resistant HER2-Positive Circulating Tumor Cells in Metastatic Breast Cancer

Abstract

Background: To evaluate the efficacy of lapatinib, a dual EGFR and HER2 tyrosine kinase inhibitor, in therapy-resistant HER2-positive CTCs in metastatic breast cancer (MBC).

Patients and methods: Patients with MBC and HER2-positive CTCs despite disease stabilization or response to prior therapy, received lapatinib 1500 mg daily in monthly cycles, till disease progression or CTC increase. CTC monitoring was performed by immunofluorescent microscopy using cytospins of peripheral blood mononuclear cells (PBMCs) double stained for HER2 or EGFR and cytokeratin.

Results: A total of 120 cycles were administered in 22 patients; median age was 62.5 years, 15 (68.2%) patients were post-menopausal and 20 (90.1%) had HER2-negative primary tumors. At the end of the second course, HER2-positive CTC counts decreased in 76.2% of patients; the median number of HER2-positive CTCs/patient also declined significantly (p = 0.013), however the decrease was significant only among patients presenting disease stabilization (p = 0.018) but not among those with disease progression during lapatinib treatment. No objective responses were observed. All CTC-positive patients harbored EGFR-positive CTCs on progression compared to 62.5% at baseline (p = 0.054). The ratio of EGFR-positive CTCs/total CTCs detected in all patients increased from 17.1% at baseline to 37.6% on progression, whereas the mean percentage of HER2-negative CTCs/patient increased from 2.4% to 30.6% (p = 0.03).

Conclusions: The above results indicate that lapatinib is effective in decreasing HER2-positive CTCs in patients with MBC irrespectively of the HER2 status of the primary tumor and imply the feasibility of monitoring the molecular changes on CTCs during treatment with targeted agents.

Trial registration: Clinical trial.gov NCT00694252.

Fig 1. CONSORT flow diagram of the study.

Fig 2. A representative picture of CTCs detected on a patient’s cytospin.

Cells were double stained using A45 B/B3 (green), HER2 (red) antibodies, and DAPI (blue) and evaluated by immunofluorescence microscopy. Presented is a HER2-negative CTC in comparison with two HER2-positive CTCs.

Fig 3. Waterfall plot of the % change in HER2-positive CTC numbers in patients treated with lapatinib (n = 20) after the completion of the first treatment cycle as compared to the baseline; in one patient no information on CTC counts was available.

Fig 4. Patient-specific trajectories of HER2-positive CTCs during the first 8 cycles of treatment.

The trajectories of CTCs are marked red in patients that discontinued treatment due to increase in CTC counts (n = 6), green in cases with disease progression (n = 12) and blue for both CTC increase and disease progression (n = 1). One patient withdrew consent (depicted in yellow) and one was still on treatment at the time of the analysis (purple).

Fig 5. Box-plot of total HER2-positive CTC counts detected in the whole group of patients at baseline and after the completion of the first and second treatment cycles.

Shown are the median values ± SD of HER2-positive CTC numbers. HER2-positive CTCs declined from a median of 130 per patient (range 1–617), to a median of 2 (range 0–542) (p = 0.103) and 2 per patient (range 0–513) at the end of the first and second treatment courses, respectively (p = 0.013). Boxes represent the 25^th and 75^th percentile; line within the box shows the median value (Whiskers: Tukey).

Fig 6. Kaplan-Meier estimate of Progression-Free-Survival (PFS) in patients with metaststic breast cancer receiving lapatinib (n = 21).

Fig 7. Box-plot of total HER2-positive CTC counts detected in patients with stable disease (A) and progressive disease (B) as best response to treatment at baseline and after the completion of the first and second treatment cycles.

Shown are the median values ± SD of HER2-positive CTC numbers. In patients with stable disease CTCs declined from a median of 105 per patient (range 10–305) at baseline to 0 (range 0–500) and 0 (range 0–175), post-first (p = 0.193) and post-second cycles (p = 0.018), respectively. No significant differences in CTC counts were observed in patients with progressive disease. Boxes represent the 25^th and 75^th percentile; line within the box shows the median value (Whiskers: Tukey).