The French UNICANCER-PACS 01 trial compared six cycles of anthracycline-based adjuvant therapy with FEC (epirubicin, cyclophosphamide, fluorouracil; FEC6) vs three cycles of FEC followed by three cycles of docetaxel (FEC/docetaxel) in patients with node-positive primary breast cancer. After adjuvant therapy, patients with hormone receptor–positive disease received endocrine therapy. Radiation therapy was recommended for all patients with conservative surgery and was performed at the investigator’s discretion after mastectomy. Patients with HER2-overexpressing disease did not receive trastuzumab (Herceptin) in the adjuvant setting. The trial showed that the addition of docetaxel reduced risk of relapse by 17%.1
A biomarker analysis of the trial, recently reported by Ladoire and colleagues in Annals of Oncology, indicates that overall survival was significantly improved in patients with tumors expressing FOXP3 compared with patients with FOXP3-negative tumors, among those who received the anthracycline-based adjuvant therapy without docetaxel.2
FOXP3, first identified as a transcription factor involved in the development and function of regulatory T cells, has been found in cancer cells and has been variously reported to be both a poor prognostic factor in breast cancer and a tumor-suppressor gene that acts as a transcriptional repressor of oncogenes such as HER2 and Skp2. In an earlier study, Ladoire and colleagues found that FOXP3 expression was predictive of improved survival in a small retrospective series of patients with breast cancer receiving neoadjuvant therapy, with data suggesting the difference in effect occurred in patients receiving anthracyclines but not in those receiving taxanes. Other recent studies indicated that FOXP3 expression might be associated with sensitivity to DNA-damaging agents and topoisomerase inhibitors.
Analysis of FOXP3
In the current analysis,2 the investigators found that 405 (36.9%) of 1,097 evaluable tumor samples from the PACS 01 study were FOXP3-positive. Tumor blocks were initially collected from 1,190 of the 1,999 patients in the trial. Clinical characteristics did not differ between patients tested for FOXP3 expression and those not tested, except for a greater frequency of T2 and T3 disease in the latter.
Of the 1,097 evaluable patients, half had received FEC6 alone and half FEC/docetaxel. Among the 405 FOXP3-positive patients, 53.1% had received FEC/docetaxel; among the 692 FOXP3-negative patients, 48.4% had received FEC/docetaxel. Overall, 16% of patients had HER2-overexpressing tumors, including 14.1% of the FOXP3-positve group and 17.5% of the FOXP3-negative group.
Patients with FOXP3-positive tumors were significantly more likely to have a lower tumor grade (I/II in 64.6% vs 50.5%, P < .001) and fewer involved nodes (1 to 3 in 67.2% vs 59.4%, P = .026), and were significantly less likely to have distant metastasis (19.5% vs 28%, P = .002) and to die (15.3% vs 22.5%, P = .004). The two groups did not differ with regard to HER2 status, treatment group distribution, T stage, hormone receptor status, locoregional relapse, or contralateral relapse.
Survival Reduced in FOXP3-negative Patients
On univariate analysis, factors associated with shorter survival were HER2 overexpression, high number of involved nodes, high tumor grade, hormone receptor–negative status, T stage, FEC6 treatment group, and FOXP3-negative status (hazard ratio [HR] = 1.59, P = .003). Subgroup univariate analysis according to FOXP3 status and treatment arm showed that FOXP3 status was associated with shorter survival only in the FEC6 group—ie, overall survival was significantly shorter for FOXP3-negative patients in the FEC6 group (P = .0005). Survival rates at 8 years were 83% in FOXP3-positive patients receiving FEC6 compared with 75% in FOXP3-negative patients receiving FEC6, and 89% in FOXP3-positive patients receiving FEC/docetaxel compared with 86% in FOXP3-negative patients receiving FEC/docetaxel.
On multivariate analysis, T stage, higher number of involved nodes, and high tumor grade remained independently associated with shorter survival. FOXP3-negative status also remained independently predictive of shorter survival, but only in the FEC6 arm (P = .011). Compared with this subgroup, risk of death was significantly reduced to a similar degree in the FOXP3-negative plus FEC/docetaxel (HR = 0.62, P = .008), FOXP3-positive plus FEC6 (HR = 0.62, P = .035), and FOXP3-positive plus FEC/docetaxel (HR = 0.57, P = .016) subgroups. The overall interaction between treatment and FOXP3 status was not significant (P = .4).
FOXP3 Expression Increases Anthracycline Antitumor Activity
To further assess the potential connection between FOXP3 expression and response to anthracyclines, the investigators performed studies to determine whether FOXP3 increased tumor cell sensitivity to anthracyclines in vitro. Prior studies had shown that HDAC inhibitors such as valproic acid can increase FOXP3 gene expression. The investigators found that FOXP3 expression was augmented in four of six breast cancer cell lines (HCC1954, MDA-MB-231, BT474, and HBL100, but not hs578T or MCF7) with low doses of valproic acid, with the induction of FOXP3 being associated with downregulation of Skp2 protein.
It was then found that valproic acid, which did not exert any antitumor activity alone, enhanced the cytotoxic effects of epirubicin in cell lines in which FOXP3 expression was increased and not in those in which no valproic acid–induced increase in FOXP3 expression was observed. Valproic acid treatment had no effect on the cytotoxic activity of docetaxel. In tumor cells (MDA-MB-231) knocked down for FOXP3 production (using small interfering RNA), valproic acid did not affect epirubicin activity, suggesting that the effect of valproic acid in increasing epirubicin activity was through enhanced FOXP3 expression.
As noted by the investigators, their analyses suggests that absence of FOXP3 expression in breast tumors could identify a subset of patients with anthracycline-resistant disease who potentially derive marked benefit from the addition of a taxane to adjuvant therapy. The findings also emphasize the antioncogenic properties of the FOXP3 protein and recommend it as a target for future interventions in breast cancer.
The investigators concluded, “[T]hese results strengthen the importance of the analysis of FOXP3 expression in patients with breast cancer, as such information can be used as an additional tool for the stratification of patients in clinical trials evaluating the benefits of taxanes or anthracyclines. It could also help clinicians for the selection of patients who would potentially derive the highest benefit from adding docetaxel in adjuvant chemotherapy and of patients who might benefit from additional therapies, like HDAC inhibitors, such as valproic acid, in future clinical trials.” ■
1. Roche H, Fumoleau P, Spielmann M, et al: Sequential adjuvant epirubicin-based and docetaxel chemotherapy for node-positive breast cancer patients: The FNCLCC PACS 01 trial. J Clin Oncol 24:5664-5671, 2006.
2. Ladoire S, Mignot G, Dalban C, et al: FOXP3 expression in cancer cells and anthracyclines efficacy in patients with primary breast cancer treated with adjuvant chemotherapy in the phase III UNICANCER-PACS 01 trial. Ann Oncol 23:2552-2561, 2012.