Patients
The Japanese population consisted of 140 randomly assigned patients (RAM + PTX arm, 68 patients; PL + PTX arm, 72 patients). The Western population consisted of 398 randomly assigned patients from Australia, Europe, Israel, and the USA (RAM + PTX arm, 198 patients; PL + PTX arm, 200 patients).
Figure 1 shows the trial profile in the Japanese and Western populations from RAINBOW. Baseline patient and tumor characteristics were generally balanced between the treatment arms within each population. Several characteristics were unequally distributed between the Japanese and Western populations (Table 1). The percentage of patients with the following characteristics was higher in the Japanese population: ECOG PS 0, TTP from the start of first-line therapy of 6 months or more, progression during first-line therapy, gastric cancer (vs gastroesophageal junction cancer), zero to two metastatic sites (vs three or more), presence of ascites, diffuse-type adenocarcinoma, and prior doublet treatment.
Table 1 Patient and tumor characteristics of the intent-to-treat population at the baseline
The median duration of study therapy in the RAM + PTX arm was longer than in the PL + PTX arm in both populations (Japanese population, 22.5 weeks vs 12.0 weeks; Western population, 16.1 weeks vs 12.0 weeks); the longer duration of treatment relates to the longer PFS in the combination therapy arm. The median relative dose intensity of ramucirumab was 97.6 and 98.6 % in the Japanese and Western populations, respectively.
The median relative dose intensity of paclitaxel in the RAM + PTX arm was lower than that in the PL + PTX arm in the Japanese population (73.6 % vs 91.4 %), and was similar in the Western population (89.7 % vs 93.5 %). However, the median cumulative dose of paclitaxel in the RAM + PTX arm was higher than in the PL + PTX arm in the Japanese population (1026 mg/m2 vs 715 mg/m2) and the Western population (802 mg/m2 vs 599 mg/m2).
Safety
The safety population in this subgroup analysis comprised 139 patients from Japan (RAM + PTX arm, 68 patients; PL + PTX arm, 71 patients) and 393 patients from the West (RAM + PTX arm, 196 patients; PL + PTX arm, 197 patients). The commonest treatment-emergent adverse events (TEAEs) of any grade occurring with a higher incidence in the RAM + PTX arm compared with the PL + PTX arm in both populations included fatigue, neutropenia, neuropathy, decreased appetite, and epistaxis (Table 2). The incidence of TEAEs of grade 3 or higher was higher in the RAM + PTX arm than in PL + PTX arm in both populations (Japanese population, 83.8 % vs 52.1 %; Western population, 79.1 % vs 61.9 %).
Table 2 Treatment-emergent adverse events (TEAEs)
Neutropenia was the commonest TEAE of grade 3 or higher occurring with a higher incidence in the RAM + PTX arm than in the PL + PTX arm in both populations (Japanese population, 66.2 % vs 25.4 %; Western population, 32.1 % vs 14.7 %). The incidence of febrile neutropenia was low and similar between treatment arms (RAM + PTX vs PL + PTX) in both populations (Japanese population, 4.4 % vs 4.2 %; Western population, 2.6 % vs 1.5 %).
With the exception of hypertension, all adverse events of special interest of grade 3 or higher were reported with an incidence of less than 5 % across treatment arms and populations (Table 2). The incidences of grade 3 or higher bleeding/hemorrhage (Japanese population, 4.4 % vs 1.4 %; Western population, 4.6 % vs 1.5 %) and gastrointestinal perforation (Japanese population, 1.5 % vs 0.0 %; Western population, 1.0 % vs 0.0 %) were higher in the RAM + PTX arm than in the PL + PTX arm and were similar in both populations. Grade 3 proteinuria (RAM + PTX vs PL + PTX) was reported only in the Japanese population (4.4 % vs 0.0 %). Grade 3 hypertension was more frequently reported in the Western population (Japanese population, 4.4 % vs 0.0 %; Western population, 18.9 % vs 2.5 %). No grade 3 or higher proteinuria or hypertension was reported in the Japanese population or the Western population.
The percentage of patients in the Japanese population who experienced at least one serious adverse event was similar between the treatment arms (RAM + PTX vs PL + PTX) and lower than in the Western population [Japanese population, 22.1 % (15) vs 26.8 % (19); Western population, 53.6 % (105) vs 43.7 % (86)]. The incidence of TEAEs leading to death was similar between the treatment arms for both the Japanese population [1.5 % (1) vs 2.8 % (2)] and the Western population [12.8 % (25) vs 19.3 % (38)].
Treatment discontinuation
Disease progression was the commonest reason for treatment discontinuation in both treatment populations (Fig. 1): 88.2 and 84.7 % of patients in the Japanese population (RAM + PTX arm and PL + PTX arm, respectively), and 69.7 and 71.5 % of patients in the Western population (RAM + PTX arm and PL + PTX arm, respectively). The second commonest reason for treatment discontinuation was adverse events, occurring in 7.4 and 8.3 % of patients in the Japanese population (RAM + PTX arm and PL + PTX arm, respectively) and in 13.6 and 13.5 % of patients in the Western population (RAM + PTX arm and PL + PTX arm, respectively).
Post-discontinuation therapy
Whereas the rate of PDT was balanced between the two treatments arms in both populations, the rate of PDT was higher in the Japanese population (75.0 %) than in the Western population (37.2 %). Additionally, a greater proportion of patients in the Japanese population (25.0 % in the RAM + PTX arm and 34.7 % in the PL + PTX arm) received fourth-line therapy or subsequent lines of therapy compared with in the Western population (13.6 % in the RAM + PTX arm and 7.0 % in the PL + PTX arm). The most commonly used chemotherapy agents in both populations included irinotecan, taxanes, fluoropyrimidines, and platinum compounds.
Efficacy
OS, PFS, and ORR for the Japanese and Western populations are summarized in Fig. 2 and Table 3.
Table 3 Objective tumor response
In the Japanese population, the HR for OS was 0.88 (95 % CI, 0.60–1.28). The median survival was 11.4 months [interquartile range (IQR), 7.9–19.4 months] in the RAM + PTX arm versus 11.5 months (IQR, 4.8–18.9 months) in the PL + PTX arm (Fig. 2a). The 6-month survival rate was 94.1 % in the RAM + PTX arm versus 71.4 % in the PL + PTX arm in the Japanese population. In the Western population, the HR for OS was 0.73 (95 % CI, 0.58–0.91). The median survival was 8.6 months (IQR, 4.7–13.6 months) in the RAM + PTX arm versus 5.9 months (IQR, 3.1–11.0 months) in the PL + PTX arm (Fig. 2b). The 6-month survival rate was 66.0 % in the RAM + PTX arm versus 49.0 % in the PL + PTX arm in the Western population.
The OS by PDT use is shown in Fig. 3. Independent of the treatment arm, patients who did not receive PDT had shorter survival than patients who received any PDTs. In patients who did not receive PDT, there was a clear difference in OS between the two treatment arms (Fig. 3a, b), whereas in patients who received any PDT, the difference in survival was smaller (Fig. 3c, d) in both the Japanese population and the Western population.
In the Japanese population, the median PFS was 5.6 months in the RAM + PTX arm versus 2.8 months in the PL + PTX arm (HR, 0.50; 95 % CI, 0.35–0.73; Fig. 2c). In the Western population, the median PFS was 4.2 months in the RAM + PTX arm versus 2.8 months in the PL + PTX arm (HR, 0.63; 95 % CI, 0.51–0.79; Fig. 2d).
In the Japanese population, the ORR was 41.2 % (95 % CI, 30.3–53.0 %) in the RAM + PTX arm versus 19.4 % (95 % CI, 12.0–30.0 %) in the PL + PTX arm, and the DCR was 94.1 % (95 % CI, 85.8–97.7 %) in the RAM + PTX arm versus 75.0 % (95 % CI, 63.9–83.6 %) in the PL + PTX arm (Table 3). In the Western population, the ORR was 26.8 % (95 % CI, 21.1–33.3 %) in the RAM + PTX arm versus 13.0 % (95 % CI, 9.0–18.4 %) in the PL + PTX arm, and the DCR was 76.8 % (95 % CI, 70.4–82.1 %) in the RAM + PTX arm versus 56.5 % (95 % CI, 49.6–63.2 %) in the PL + PTX arm (Table 3).
In the Japanese population, almost all of the patients in the RAM + PTX arm had tumor size reductions, as did most of the patients in the Western population, as shown in the waterfall plot in Fig. 4.
Quality of life and performance status
In the Japanese population, the percentages of patients reporting stable or improved quality-of-life scores were similar between the treatment arms at week 6 and at the end of treatment, but were higher in the RAM + PTX arm than in the PL + PTX arm at all other postbaseline assessments. In the Western population, the percentages of patients reporting stable or improved quality-of-life scores were higher in the RAM + PTX arm than in the PL + PTX arm for all on-study assessments, but were similar at the end of treatment. In the Japanese population, the data suggest a longer time to deterioration to an ECOG PS of 2 or higher for RAM + PTX therapy, with a HR of 0.64 (95 % CI, 0.29–1.40). In the Western population, the HR for the time to deterioration to an ECOG PS of 2 or higher was 0.89 (95 % CI, 0.64–1.22).