An important read is McAlpine H, Joubert L, Martin-Sanchez F, Merolli M, Drummond KJ. A systematic review of types and efficacy of online interventions for cancer patients. Patient Educ Couns. 2015;98(3):283-95. doi:10.1016/j.pec.2014.11.002.
It gives a good overview of what is out there. Further studies:
Beatty L, Koczwara B, Wade T. Evaluating the efficacy of a self-guided Web-based CBT intervention for reducing cancer-distress: a randomised controlled trial.Support Care Cancer. 2015. doi:10.1007/s00520-015-2867-6.
Duffecy J, Sanford S, Wagner L, Begale M, Nawacki E, Mohr DC. Project onward: an innovative e-health intervention for cancer survivors. Psychooncology. 2013;22(4):947-51. doi:10.1002/pon.3075.
Owen JE, Klapow JC, Roth DL, Shuster JL, Jr., Bellis J, Meredith R et al. Randomized pilot of a self-guided internet coping group for women with early-stage breast cancer. Ann Beh Med. 2005;30(1):54-64. doi:10.1207/s15324796abm3001_7.
Ritterband LM, Bailey ET, Thorndike FP, Lord HR, Farrell-Carnahan L, Baum LD. Initial evaluation of an Internet intervention to improve the sleep of cancer survivors with insomnia. Psychooncology. 2012;21(7):695-705. doi:10.1002/pon.1969.
Wootten AC, Abbott JA, Meyer D, Chisholm K, Austin DW, Klein B et al. Preliminary results of a randomised controlled trial of an online psychological intervention to reduce distress in men treated for localised prostate cancer. European urology. 2015;68(3):471-9. doi:10.1016/j.eururo.2014.10.024.
Carpenter KM, Stoner SA, Schmitz K, McGregor BA, Doorenbos AZ. An online stress management workbook for breast cancer. J Behav Med. 2014;37(3):458-68. doi:10.1007/s10865-012-9481-6.
Van den Berg SW, Gielissen MF, Custers JA, van der Graaf WT, Ottevanger PB, Prins JB. BREATH: Web-Based Self-Management for Psychological Adjustment After Primary Breast Cancer-Results of a Multicenter Randomized Controlled Trial. J Clin Oncol. 2015;33(25):2763-71. doi:10.1200/JCO.2013.54.9386.
Yun YH, Lee KS, Kim YW, Park SY, Lee ES, Noh DY et al. Web-based tailored education program for disease-free cancer survivors with cancer-related fatigue: a randomized controlled trial. J Clin Oncol. 2012;30(12):1296-303. doi:10.1200/JCO.2011.37.2979.