Table 2.
Cox proportional hazards model evaluating progression-free survival after CDKi discontinuation.
| Clinical characteristic | Median PFS (95% CI), months | HR (95% CI) | P-value |
|---|---|---|---|
| Age at CDKi discontinuation | N/A | 0.99 (0.98-1.01) | .359 |
| Age at CDKi discontinuation (binary) | |||
| <65 years^ | 5.8 (5.0-7.9) | 1.07 (0.75-1.52) | .709 |
| ≥65 years | 7.0 (5.0-8.0) | ||
| De novo metastatic breast cancer | |||
| No^ | 6.9 (5.5-8.0) | 1.33 (0.89-1.99) | .160 |
| Yes | 5.3 (3.8-7.0) | ||
| Metastasis type (at time of metastatic diagnosis) | |||
| Non-visceral^ | 7.3 (5.8-8.5) | 1.35 (0.95-1.92) | .097 |
| Visceral† | 5.6 (4.6-7.4) | ||
| Pre-CDKi therapy in metastatic setting | |||
| No^ | 7.1 (5.8-8.0) | 1.06 (0.73-1.54) | .767 |
| Yes | 5.6 (5.0-7.8) | ||
| Pre-CDKi chemo in metastatic setting | |||
| No^ | 7.1 (5.8-8.2) | 1.36 (0.92-2.01) | .120 |
| Yes | 5.0 (3.8-6.1) | ||
| Pre-CDKi anastrozole in metastatic setting | |||
| No^ | 6.1 (5.0-7.3) | 0.71 (0.44-1.15) | .162 |
| Yes | 8.8 (5.0-13.0) | ||
| Pre-CDKi letrozole in metastatic setting | |||
| No^ | 7.0 (5.8-8.5) | 1.12 (0.78-1.61) | .539 |
| Yes | 5.0 (4.5-7.8) | ||
| Pre-CDKi exemestane in metastatic setting | |||
| No^ | 6.5 (5.0-7.4) | 1.05 (0.69-1.61) | .817 |
| Yes | 6.2 (4.6-9.0) | ||
| Pre-CDKi fulvestrant in metastatic setting | |||
| No^ | 6.2 (5.0-7.3) | 0.84 (0.57-1.23) | .362 |
| Yes | 7.6 (5.0-11.0) | ||
| Pre-CDKi tamoxifen in metastatic setting | |||
| No^ | 6.9 (5.6-7.9) | 1.34 (0.75-2.40) | .316 |
| Yes | 5.0 (2.9-5.8) | ||
| Pre-CDKi everolimus in metastatic setting | |||
| No^ | 6.5 (5.3-7.6) | 1.35 (0.78-2.37) | .287 |
| Yes | 5.1 (0.8-11.0) | ||
| Pre-CDKi capecitabine in metastatic setting | |||
| No^ | 6.9 (5.5-7.9) | 1.30 (0.84-2.01) | .236 |
| Yes | 5.0 (3.2-8.0) | ||
| Time between metastatic diagnosis and start of CDKi therapy, months | N/A | 1.00 (0.99-1.00) | .912 |
| Type of CDKi (first regimen) | |||
| Palbociclib^ | 6.1 (5.0-7.4) | ||
| Ribociclib | 11.7 (6.5-NA) | 0.73 (0.23-2.29) | .585 |
| Abemaciclib | 4.6 (2.2-NA) | 0.91 (0.34-2.48) | .860 |
| Endocrine therapy (specific) during CDKi‡ | |||
| Letrozole | 6.3 (5.0-8.2) | Unreliable Cox model estimates due to small category counts | |
| Fulvestrant | 6.1 (4.9-7.8) | ||
| Anastrozole | 10.7 (2.2-NA) | ||
| Tamoxifen | 7.9 (NA-NA); n = 1 | ||
| None | 2.6 (NA-NA); n = 1 | ||
| Exemestane | N/A; n = 0 | ||
| Endocrine therapy (group) during CDKi‡ | |||
| NSAI^ | 6.5 (5.0-8.4) | 1.36 (0.94-1.96) | .105 |
| SERD | 6.1 (4.9-7.8) | ||
| Duration of CDKi* | |||
| <12 months^ | 5.8 (4.8-6.5) | 0.70 (0.48-1.03) | .073 |
| ≥12 months | 8.0 (5.6-11.0) | ||
| Reason for CDKi discontinuation | |||
| Non-progression^ | 11.3 (4.6-19.4) | 2.53 (1.50-4.26) | .001 |
| Progression | 6.0 (5.0-7.1) | ||
| Type of post-CDKi therapy (TVC)** | |||
| Chemotherapy^ | 6.1 (4.8-8.0) | ||
| Endocrine tx | 5.0 (4.1-11.0) | 0.78 (0.49-1.22) | |
| CDKi | 6.9 (5.1-NA) | 0.83 (0.30-2.29) | |
| Other targeted tx | 6.3 (3.5-7.9) | 1.19 (0.75-1.87) | |
| None^ | NA (3.7-NA) | 0.54 (0.26-1.13) | |
^Reference group for interpreting the hazard ratio (HR) for PFS. If the HR in a non-reference group row is >1, this indicates that this group has a greater risk of progression or death compared to the reference group. This elevated risk is statistically significant (at the nominal α level of .05) if its 95% CI is entirely above 1
†A patient with both visceral (eg, liver) and non-visceral (eg, bone) metastases was categorized as “visceral.”
‡If a patient received >1 endocrine therapy concurrently with a CDKi, the first endocrine therapy received is represented.
*Sequential CDKi regimens were combined if the regimen switch was not due to disease progression.
**“Post-CDKi therapy” was defined as the first cancer therapy the patient received after discontinuing CDKi. However, if a CDKi regimen was discontinued due to disease progression, this “Post-CDKi therapy” could include a different, subsequent CDKi. For patients who received drugs in >1 listed category, the following precedence rules were applied (from highest precedence to lowest): chemotherapy, CDKi or other targeted therapy, endocrine therapy.
Abbreviations: NSAI, non-steroidal aromatase inhibitor; SERD, selective estrogen receptor degrader (ie, fulvestrant); TVC, time-varying covariate (ie, predictor).