Mobile Health and Social Media Physical Activity Intervention Among Adolescent and Young Adult Childhood Cancer Survivors, the StepByStep Study

Inclusion Criteria: * First diagnosis of malignant neoplasm (International Classification of Diseases for Oncology \[ICD-O\] behavior code of "3") in first and continuous remission at the time of enrollment * Curative cancer treatment must have included chemotherapy (including cellular therapy) and/or radiation (including radioactive iodine) * Note: Childrens Oncology Group (COG) therapeutic trial participation is not required * All cancer treatment must have been completed within 3-36 calendar months prior to enrollment * Patients must have a life expectancy of \> 1 year * Self-report of \< 420 minutes of moderate-to-vigorous physical activity per week as assessed via the study-specific Physical Activity Worksheet * Note: See COG Study Web Page for the Godin-Shephard Leisure Time Physical Activity Questionnaire or link to online calculator * Ambulatory and no known medical contraindications to increasing physical activity * Note: Patients with amputation, rotationplasty, or other prothesis are not automatically excluded as long as they are ambulatory and have no known medical contraindications to increasing physical activity and all other eligibility criteria are satisfied * No known significant physical or cognitive impairment that would prevent use of the electronic devices used for the protocol intervention (e.g. Fitbit, smartphone, tablet, or computer) * Able to read and write English * Note: For patients \< 18 years, consenting parent/legal guardian does not have to be able to read and write English * All patients and/or their parents or legal guardians must sign a written informed consent * Note: Informed consent may be obtained electronically/online if allowed by local site policy and Institutional Review Board (IRB)/Research Ethics Board (REB) of record * All institutional, Food and Drug Administration (FDA), and National Cancer Institute (NCI) requirements for human studies must be met Exclusion Criteria: * Post-menarchal female patients who are pregnant or planning to become pregnant in the next year are excluded * Note: Pregnancy status can be established by clinical history with patient. Post-menarchal female patients are eligible as long as they agree to use an effective contraceptive method (including abstinence) during study participation * Patients with previous hematopoietic stem cell transplant (HSCT) are excluded * Note: Patients with previous autologous HSCT, chimeric antigen receptor T-cell (CAR T-cell) therapy, and other cellular cancer therapies can participate as long as all other eligibility criteria are satisfied