Cancer-related subreddits: A comprehensive survey and correlation of membership and tumor subtype prevalence, incidence, and survival.
Authors: Shakespeare Christopher S. , O'Keefe Ryan M , Caputo Kendra L. , Archambeault Marcella G. , Elaba Kevin P. , Wall Diana A. , Hill-Kayser Christine E. 
Published: June 2021

e23012 Background: Reddit is an anonymous, international, social media platform with 430 million active users; most are age 18-40 and a majority are male. Its discussion-based format is well-suited to healthcare, allowing patients, loved ones, and healthcare providers (HCPs) to interact, and numerous medical-focused “subreddit” (SR) communities exist. Previous work has analyzed SR topics including breast cancer, radiation therapy, COVID-19, and depression. To date, no comprehensive list of cancer-related SRs has been compiled or analyzed. Methods: Between 1/7/21 and 2/10/21, a list of cancer-related keywords were queried on reddit.com, SRs were identified, and information was coded from their homepages; final membership numbers were updated on 2/10/21. Tumor subtypes included those listed on the SEER website (seer.cancer.gov/statfacts) where data on prevalence, annual incidence, death, and 5-year survival were pulled. Historical SR membership data was determined using subredditstats.com. Descriptive stats, Pearson’s correlation, and regression were performed using R software and Excel. Results: 36 cancer-related SRs were identified: 31 (86.1%) active in last 6 months, 17 (47.2%) with daily activity, 24 (66.7%) focused on tumor subtypes, 9 (25.0%) for general support and discussion, and 3 (8.3%) focused on treatment modalities. Median time since inception of SRs was 6 years (range 1 – 12), median number of members was 739 (range 42 – 36519), and median number of moderators was 2 (range 1 – 8). 16 (44.4%) had formal rules for members. Only 1 (2.7%) prohibited those without cancer from posting. Among the groups with > 500 members (25, 69.4%), median growth since 1/1/20 was 66% (range 10 – 370%). 16 (59.3%) of the 27 SEER tumor sub-types were represented by a SR, 5 (18.5%) of which had more than one SR, and 14 (51.8%) had > 500 members. Correlation and R Square via regression between tumor subtype prevalence, annual incidence, deaths, and 5-year survival and associated SR members was 0.61 and 0.368 (p = 0.02), 0.45 and 0.199 (p = 0.11), -0.07 and 0.005 (p = 0.82), 0.33 and 0.107 (p = 0.26), respectively. Based on the prevalence regression line, over-represented tumor subtypes include brain, testicular, and lymphoma. Under-represented sub-types include cervical, ovarian, colon/rectal, prostate, and lung. Conclusions: SRs represent rapidly growing online communities for those with cancer to seek information and support. Many tumor subtypes are represented; however, some common cancers are either not represented (renal, liver, stomach, endometrial) or underrepresented (colon, prostate, lung). The demographic makeup of Reddit users may explain the over-representation of brain, testicular, and lymphoma, as they can arise in younger patients, particularly men. Future work should assess the content of specific SRs and investigate the role of anonymous HCP input.