Social Media Discourse on Breast Cancer Screening Barriers in Japanese and English: Cross-Sectional Infodemiology Study.

Background: Despite clinical advances, breast cancer screening adherence remains stagnant in Japan (<50%) compared with the United States (>70%). Understanding distinct cross-cultural barriers is essential; however, traditional methodologies often fail to capture visceral, real-world individual experiences and hidden deterrents to screening. Objective: This study aims to characterize and compare cross-cultural informatics profiles of barriers to breast cancer screening across Japanese-language and English-language social media discourse. Methods: We developed an automated natural language processing pipeline on a cloud-based informatics platform to analyze 46,823 screening-related posts (30,027 in Japanese and 16,796 in English) from X (formerly Twitter) collected in 2025, derived from an initial 76,955 posts after noise exclusion. The methodology integrated large language model-assisted sentiment polarity scoring with strict negation-handling, co-occurrence network topology analysis, and advanced distributional visualizations, including raincloud and ridgeline plots. Subgroup comparisons (prescreening vs postscreening and ultrasound with vs without mammography) were evaluated. Results: Among the 46,823 screening-related posts, overall sentiment distributions showed no practically meaningful cross-cultural divergence (Cohen d=0.049); however, domain-specific analyses revealed sharp disparities in barrier prevalence. Within the English-language cohort containing 16,796 posts, discourse exhibited a concentrated, moderate negative sentiment regarding systemic barriers, featuring "Cost" as the primary barrier (n=1239, 7.4%), while "Pain" ranked considerably lower (n=842, 5.0%). In contrast, the Japanese-language cohort containing 30,027 posts was heavily bottlenecked by psychosomatic barriers, governed by a tightly interconnected network of "Pain," "Fear," and "Appointment." "Pain" emerged as the overwhelmingly dominant barrier (n=5788, 19.3%). In the English-language cohort, "Dense" breasts emerged as a prominent clinical topic due to elevated public awareness, distinct from the financial narrative. The Japanese subgroup analyses identified a temporal transition from anticipatory psychological anxiety ("Fear," 739/3805, 19.4%) and logistical concerns ("Appointment," 1556/3805, 40.9%) before screening to a strong persistence of the discomfort memory of "Pain" (1160/7419, 15.6%). Furthermore, sentiment scores for mammography were significantly more negative than those for ultrasound alone (P<.001, Cohen d=0.264), and pain-related descriptors for ultrasound spiked from 5.0% (106/2110, ultrasound alone) to 18.2% (733/4017) when performed concurrently with mammography. Conclusions: Despite comparable overall emotional equilibrium, a fundamental dichotomy emerged. The English-language discourse predominantly reflects US-specific systemic financial burdens, whereas the Japanese experience is characterized by emotional volatility transitioning from anticipatory anxiety to a tightly interconnected "Pain-Fear-Appointment" network. Physical discomfort of mammography dominates the screening narrative, overshadowing concurrent painless modalities like ultrasound. Improving adherence in Japan requires individualized pain-mitigating compression protocols and optimized clinical workflows to decouple mammographic discomfort from supplemental screening, thereby preventing pain-associated defensive avoidance and reducing logistical hurdles to improve equitable access.