BACKGROUND: Breakthrough cancer pain (BTcP) is a predictor of interference with general activities and poor pain management. The extent of this influence has not yet been determined. OBJECTIVE: This study aimed to investigate the influence of BTcP on general activities, and pain management in patients with controlled background pain. DESIGN: Single-center prospective observational study. SETTING/SUBJECTS: The study cohort comprised 258 consecutive patients (female, 40.0%; mean age, 64.5 years) who had received opioid medication for cancer pain for over 2 weeks. MEASUREMENTS: A recommended diagnostic algorithm was used to quantitate and compare interference with general activities, average background pain intensity over the previous 24 hours (24h-PI), and achievement of personalized pain goals (PPGs) (24h-PI≤PPG) of 119 patients with and 139 patients without BTcP. RESULTS: Interference with general activities, 24h-PI, and PPG scores [mean (standard deviation)] in patients with BTcP were 2.8 (2.2), 3.0 (1.7), and 1.8 (1.4), respectively, which are all significantly higher than for those without BTcP [1.3 (2.0), p < 0.01; 1.7 (1.6), p < 0.01; 1.5 (1.3), p = 0.03], respectively. A significantly smaller percentage of patients with BTcP than without BTcP achieved their PPGs (36.1% vs. 67.6%, p < 0.01). CONCLUSIONS: BTcP has a negative impact on general activities and pain management. Healthcare providers should recognize that management of BTcP is important in improving general activities and management of cancer pain.