Online Information-Seeking Behaviour for Major Cancers: A 10-Year Infodemiological Study to Inform Public Health and Health Promotion Priorities in Hungary

Background/Objectives: To analyse trends in online information-seeking behaviour for five major cancers in Hungary, compare them with global trends, and assess changes during the COVID-19 pandemic, cancer-related awareness campaigns, and major cancer-related events on search activity. Methods: A retrospective observational infodemiological study was conducted using Google Trends™ (GT) data for lung, colorectal, breast, prostate, and pancreatic cancers between 2013 and 2022. Search intensity was assessed using uncorrected relative search volume (RSVraw) as the primary measure, complemented by RSVsens, as an Internet penetration-adjusted sensitivity analysis. Descriptive statistics, parametric tests, time-series and seasonality analyses, Mann–Kendall tests, and joinpoint regression were performed using IBM SPSS Statistics 22.0, PAST 4.03, and Joinpoint 5.3.0 (α: 0.05; 95% confidence interval [CI]). Benjamini–Hochberg (BH) false discovery rate (FDR) correction was applied for multiple testing. Results: Among the cancer types relevant to our study, lung and breast cancer showed the highest reference-adjusted RSV (RSVref: 61) in Hungary, followed by prostate (RSVref: 59), colorectal (RSVref: 52), and pancreatic cancer (RSVref: 11); whereas globally, breast cancer ranked first (RSVref: 49). RSVsens showed significant decreasing trends for all five cancer types (Mann–Kendall, all p < 0.05), with average annual percentage changes (AAPCs) of −5.39% for lung, −4.06% for breast, −3.56% for colorectal, −3.59% for prostate, and −5.23% for pancreatic cancer, respectively (all p < 0.05). Breast and prostate cancers exhibited significant (p < 0.001) and recurring seasonal peaks. During COVID-19 (vs. the pre-pandemic period), mean RSV values decreased by 10–30% across all cancers; only colorectal cancer-related campaigns were associated with a notable increase in search intensity (+66.9%, p = 0.013, q = 0.058), although this association did not remain significant after FDR correction.. Symptom-related searches predominated, whereas screening- and prevention-related queries were infrequent during the study period. Conclusions: GT may be a useful complementary tool for monitoring public interest and evaluating public health communication. The absence of consistent increases in search activity during most campaign periods, together with the predominance of symptom-related queries, suggests that current communication initiatives may have limited measurable visibility in GT search behaviour and highlights the need to strengthen communication on cancer prevention and early detection.