ドセタキセル再挑戦 vs カバジタキセル：転移性去勢抵抗性前立腺がんにおける適切なタキサン系薬剤の選択

Highlights

The comparative effectiveness of taxane therapies in metastatic castration-resistant prostate cancer (mCRPC) has long been a subject of clinical debate. Key findings from this recent Veterans Affairs cohort study include:

• Patients undergoing docetaxel rechallenge experienced a significantly longer median overall survival (12.3 months) compared to those treated with cabazitaxel (9.6 months).
• The hazard ratio for death in the docetaxel rechallenge group was 0.81 (95% CI, 0.55-0.99; P = .04) relative to the cabazitaxel group.
• A higher proportion of patients in the docetaxel rechallenge group achieved a 90% or greater reduction in prostate-specific antigen (PSA) levels (9.8% vs 3.0%).
• The findings suggest that for patients who maintain sensitivity to initial docetaxel therapy, rechallenge may be a superior clinical strategy over switching to cabazitaxel.

Background and Clinical Context

Since the landmark TAX 327 and SWOG 9916 trials in 2004, docetaxel has served as the foundational cytotoxic chemotherapy for metastatic castration-resistant prostate cancer (mCRPC). It was the first agent to demonstrate a survival benefit in this population, effectively inhibiting microtubule depolymerization and inducing apoptosis in malignant cells. In 2010, the TROPIC trial introduced cabazitaxel—a semi-synthetic derivative of a natural taxoid—as an effective second-line taxane for patients who progressed during or after docetaxel treatment.

While the sequencing of these agents is well-established for patients who exhibit resistance to docetaxel, a clinical gray area exists for those who previously responded well to docetaxel and completed their initial course without evidence of disease progression. In such cases, clinicians must choose between rechallenging with docetaxel or transitioning to cabazitaxel. Until now, high-level comparative evidence to guide this decision has been scarce, often leaving treatment choices to physician preference or institutional protocol.

Study Design and Methodology

This study utilized a retrospective cohort design, leveraging the comprehensive electronic health records of the nationwide Veterans Affairs (VA) health care system. The study period spanned from January 1, 2010, to December 31, 2023, providing over a decade of longitudinal data.

Participant Selection

The researchers identified 669 patients with chemonaive mCRPC who received initial docetaxel treatment and did not experience disease progression during that first course. These patients were then categorized into two cohorts based on their subsequent taxane exposure: those who received a docetaxel rechallenge (n = 262) and those who switched to cabazitaxel (n = 407).

Statistical Rigor

To account for the non-randomized nature of the treatment assignment, the investigators employed inverse probability of treatment weighting (IPTW). This method uses propensity scores to balance baseline characteristics—such as age, comorbidities, and disease burden—between the two groups, mimicking the conditions of a randomized controlled trial and reducing potential selection bias.

Endpoints

The primary outcome was overall survival (OS), measured from the initiation of the second taxane course. Secondary endpoints included time to next systemic treatment or death (TTNT), and the percentage of patients achieving a PSA reduction of 50% or more (PSA50) and 90% or more (PSA90).

Key Findings: Survival and Response Metrics

The results of the analysis provide a compelling argument for the efficacy of docetaxel rechallenge in a specific patient subset.

Overall Survival (OS)

The weighted Kaplan-Meier analysis revealed a clear separation in survival curves. The docetaxel rechallenge group achieved a median OS of 12.3 months (IQR, 10.5-13.8), whereas the cabazitaxel group achieved a median OS of 9.6 months (IQR, 8.6-11.1). The resulting hazard ratio of 0.81 indicates a 19% reduction in the risk of death for those undergoing rechallenge, which was statistically significant (P = .04).

PSA Response and Disease Control

The biochemical response data further supported the survival findings. A weighted 9.8% of patients in the docetaxel rechallenge group achieved a PSA90 response, more than triple the 3.0% observed in the cabazitaxel group. Furthermore, the time to next treatment or death was longer in the rechallenge group (median 10.7 months) compared to the cabazitaxel group (8.9 months).

Subsequent Therapies

Interestingly, the study found no significant difference in the subsequent use of other advanced therapies, such as platinum-based chemotherapy, immunotherapy, or PARP inhibitors, suggesting that the survival benefit was likely derived from the choice of the second taxane itself rather than disparate access to later-line treatments.

Expert Commentary and Clinical Implications

The findings by Barata et al. challenge the prevailing trend of moving directly to cabazitaxel as the “next” taxane in all scenarios. These results suggest a “precision sequencing” approach: if a patient’s tumor remains sensitive to docetaxel—defined here by a lack of progression during the initial exposure—the biological machinery likely remains susceptible to the same mechanism of action.

Biological Plausibility

The biological rationale for these findings may lie in the mechanisms of taxane resistance. Cabazitaxel was specifically engineered to have a low affinity for the P-glycoprotein (P-gp) efflux pump, which often mediates resistance to docetaxel. However, in patients who did not progress on docetaxel, P-gp expression may not yet be the dominant resistance mechanism. Re-exposing these cells to docetaxel may maximize the therapeutic window of the first-generation taxane before moving to the second-generation agent.

Study Limitations

Despite the use of IPTW, the retrospective nature of the study remains a limitation. Unmeasured confounders, such as patient preference or subtle differences in performance status not captured in the VA records, could influence the results. Additionally, the VA population is predominantly male and may not fully represent the demographic diversity found in other healthcare systems. However, the large sample size and the use of real-world data provide significant external validity for clinicians treating similar patient populations.

Conclusion and Summary

In patients with mCRPC who previously demonstrated sensitivity to docetaxel, a rechallenge with the same agent appears to be associated with superior overall survival and better biochemical response compared to switching to cabazitaxel. This study provides crucial evidence for oncologists and urologists, suggesting that docetaxel rechallenge should be considered a standard-of-care option in the second-line setting for docetaxel-sensitive patients.

Future prospective randomized trials are needed to confirm these findings and to better define the optimal “docetaxel-free interval” that might predict success with a rechallenge strategy. For now, these data offer a clear signal that returning to a previously successful therapy can be a powerful tool in the management of advanced prostate cancer.

References

Barata PC, Corrigan JK, La J, et al. Docetaxel Rechallenge vs Cabazitaxel in Patients With Metastatic Castration-Resistant Prostate Cancer. JAMA Netw Open. 2026;9(1):e2551231. doi:10.1001/jamanetworkopen.2025.51231.

de Bono JS, Oudard S, Ozguroglu M, et al; TROPIC Investigators. Prednisone plus cabazitaxel or mitoxantrone for metastatic castration-resistant prostate cancer progressing after docetaxel treatment: a randomised open-label phase 3 trial. Lancet. 2010;376(9747):1147-1154.

Tannock IF, de Wit R, Berry WR, et al; TAX 327 Investigators. Docetaxel plus prednisone or mitoxantrone plus prednisone for advanced prostate cancer. N Engl J Med. 2004;351(15):1502-1512.