Table 1. Patient characteristics.
| Characteristics | CDK4/6i (first) | CDK4/6i (second) | Non-CDK4/6i | p1* | p2* | ||
|---|---|---|---|---|---|---|---|
| All patients | 41 | 33 | 67 | ||||
| Median age (range) | 51 (34–78) | 57 (35–81) | 63 (27–88) | 0.003 | 0.076 | ||
| Menopausal status† | 0.004 | 0.518 | |||||
| Pre- or perimenopause | 21 (51%) | 10 (30%) | 16 (24%) | ||||
| Post | 20 (49%) | 23 (70%) | 50 (75%) | ||||
| Disease stage at initial diagnosis‡ | 0.409 | 0.023 | |||||
| I | 9 (22%) | 3 (9%) | 14 (21%) | ||||
| II | 19 (46%) | 14 (42%) | 26 (39%) | ||||
| III | 6 (15%) | 5 (15%) | 18 (27%) | ||||
| IV | 7 (17%) | 11 (33%) | 7 (10%) | 0.351§ | 0.006§ | ||
| Histological type | 0.676 | 0.107 | |||||
| Invasive ductal carcinoma | 37 (90%) | 27 (82%) | 62 (93%) | ||||
| Invasive lobular carcinoma | 4 (10%) | 6 (18%) | 5 (7%) | ||||
| Histological grade‖ | 0.570 | 0.179 | |||||
| Low/Intermediate | 31 (76%) | 27 (82%) | 42 (63%) | ||||
| High | 9 (22%) | 6 (18%) | 16 (24%) | ||||
| Progesterone receptor status¶ | 0.074 | 0.871 | |||||
| Negative | 2 (5%) | 5 (15%) | 11 (16%) | ||||
| Positive | 39 (95%) | 28 (85%) | 56 (84%) | ||||
| Postoperative metastatic lymph nodes** | 0.870 | 0.624 | |||||
| Negative | 15 (37%) | 8 (24%) | 25 (37%) | ||||
| Positive | 19 (46%) | 14 (42%) | 34 (51%) | ||||
| Metastatic site at the time of relapse†† | 0.143 | 0.552 | |||||
| Visceral disease‡‡ | 25 (61%) | 13 (39%) | 29 (43%) | ||||
| Liver involvement | 14 | 6 | 9 | ||||
| Bone only | 12 (29%) | 9 (27%) | 21 (31%) | ||||
| Other | 4 (10%) | 11 (33%) | 15 (22%) | ||||
| Median DFI (range) | 44.3 (10–245) | 53.9 (3–146) | 54.0 (10–294) | 0.496 | 0.992 | ||
| ≤ 12 months | 1 (2%) | 2 (6%) | 2 (3%) | 0.637 | 0.559 | ||
| > 12 and ≤ 60 months | 21 (51%) | 11 (33%) | 31 (46%) | ||||
| > 60 months | 12 (29%) | 9 (27%) | 27 (40%) | ||||
| Prior chemotherapy for neoadjuvant or adjuvant treatment§§ | 0.835 | 0.875 | |||||
| Yes | 20 (49%) | 13 (39%) | 36 (54%) | ||||
| No | 14 (34%) | 9 (27%) | 23 (34%) | ||||
| Endocrine therapy with neoadjuvant or adjuvant treatment‖‖ | 0.059 | 0.402 | |||||
| Aromatase inhibitors | 10 (24%) | 10 (30%) | 26 (39%) | ||||
| Tamoxifen | 21 (51%) | 10 (30%) | 20 (30%) | ||||
| Aromatase inhibitors and tamoxifen | 1 (2%) | 2 (6%) | 7 (10%) | ||||
| None | 2 (5%) | 0 (0%) | 6 (9%) | ||||
| Primary endocrine therapy for metastatic disease | - | 0.394 | |||||
| Aromatase inhibitors | - | 16 (48%) | 35 (52%) | ||||
| Tamoxifen | - | 10 (30%) | 23 (34%) | ||||
| Fulvestrant | - | 7 (21%) | 7 (11%) | ||||
| Other | - | 0 (0%) | 2 (3%) | ||||
| Median PFS of first-line for metastatic disease (range) | 30.0 (0.5–44) | 11.9 (2–36) | 13.0 (1–115) | 0.027¶¶ | 0.377¶¶ | ||
| Endocrine therapy resistance | - | - | |||||
| Primary | - | 10 (30%) | - | ||||
| Secondary | - | 23 (70%) | - | ||||
| Type of CDK4/6i | - | - | |||||
| Palbociclib | 23 (56%) | 20 (61%) | - | ||||
| Abemaciclib | 18 (44%) | 13 (39%) | - | ||||
| Endocrine therapy in combination with CDK4/6i | - | - | |||||
| Aromatase inhibitors | 21 (51%) | 13 (39%) | - | ||||
| Fulvestrant | 20 (49%) | 20 (61%) | - | ||||
CDK4/6i = cyclin-dependent kinase 4 and 6 inhibitor; DFI = disease-free interval; PFS = progression-free survival.
*p1-value is the p-value of the CDK4/6i (first) group vs. that of the non-CDK4/6i group, and p2-value is the p-value of the CDK4/6i (second) group vs. that of the non-CDK4/6i group.
†Menopausal status was not available for one patient in the non-CDK4/6i group.
‡Disease stage at initial diagnosis was not available for two patients in the non-CDK4/6i group.
§p1- and p2-values indicate the p-value of non-stage IV versus stage IV in each group.
∥Histological grade was not available for one and nine patients in the CDK4/6 (first) and non-CDK4/6i groups, respectively.
¶Allred scores of 3–8 are considered positive.
**Number of postoperative metastatic lymph node was not available for one patient in the non-CDK4/6i group.
††Metastatic sites were not available for two patients in the non-CDK4/6i group.
‡‡Viscera refers to the lungs, liver, pleura, and adrenal glands.
§§Prior chemotherapy for neoadjuvant or adjuvant treatment was not available for one patient in the non-CDK4/6i group.
∥∥Endocrine therapy with neoadjuvant or adjuvant treatment was not available for one patient in the non-CDK4/6i group.
¶¶Median PFS after first-line treatment for metastatic disease was assessed using the generalized Wilcoxon test.