This study aims to recruit post-treatment breast cancer survivors for a 12-week 2-arm randomized walking intervention. All intervention materials will be delivered electronically.

The investigators hypothesize that at the end of 12-weeks, participants randomized to the intervention group will engage in more weekly steps than those participants randomized to the comparison group.

More than two-thirds of breast cancer survivors are physically inactive. Inactivity is known to negatively impact both morbidity and mortality, and is especially pronounced among cancer survivors. Self-directed interventions targeting inactivity among breast cancer survivors often report clinically insignificant behavior change. More successful behavior change interventions have suggested that tailoring and, more recently, the fostering of intrinsic motivation, may have improved outcomes. However, no interventions to date have utilized these approaches to increase physical activity among sedentary cancer survivors.

AIM 1: Develop and test intervention (tailored) and comparison group (targeted) messages in a sample of sedentary women to determine message acceptability.

AIM 2: Determine the efficacy of a 12-week tailored intervention to increase the number of weekly steps taken among sedentary post-treatment breast cancer survivors compared to a 12-week, targeted intervention.

Inclusion Criteria:

• Female
• 40-70 years of age
• History of breast cancer stage I-II
• 2-10 years post-treatment
• Sedentary
• Technology access and skills
• Regular access to personal computer/ broadband internet and email account
• Comfortability using internet, and web-based tools
• US Resident

Exclusion Criteria:

• Concurrent enrollment in another physical activity/ lifestyle/ weight loss intervention program/study
• Current secondary cancer diagnosis/ treatment
• Inability to ambulate
• Refusal to wear personal activity monitor (FitBit Ultra) for the duration of the study
• Engaging in regular moderate to vigorous physical activity