There is "strong" evidence that physical activity (PA) can reduce the risk of breast cancer (Bernstein, 2009; Kehm et al., 2020), which is important for individuals at higher-than-average risk due to their family history or genetic susceptibility. PA can also enhance quality of life (QoL), fitness, and surrogate markers (e.g., weight) linked to cancer prognosis (Ligibel et al., 2019; Patel et al., 2019). Despite this evidence, most adults are insufficiently active, meaning they do not meet Canadian recommendations of at least 150 minutes of PA each week (Statistics Canada, 2020). This study aims to develop materials that can help increase the number of adults at higher-than-average risk who meet PA recommendations, alongside improving QoL and body mass index (BMI; a measure of one's body weight-height ratio). Participants will include individuals assigned female at birth, aged 30-69 years, at high-risk of breast cancer registered in the Ontario Breast Screening Program who will be randomly assigned to receive (1) the intervention, which includes a copy of PA recommendations (Canadian Society for Exercise Physiology [CSEP] recommendations for adults plus content spotlighting PA benefits) plus a PA motivation package featuring three online webinars (explaining PA benefits and how to get started), digitized PA materials (providing evidence-based tools to modify behaviour), and a digitized logbook (to track PA) or (2) only a copy of PA recommendations.

Considerable research (>500 studies) has examined the association between physical (in)activity and cancer incidence (Friedenreich et al., 2021; McTiernan et al., 2019; McTiernan et al., 1999; Patel et al., 2019). Reviews of observational studies have led to the conclusion that there is some evidence for a reduced risk of 11 different cancer sites when comparing the highest to the lowest levels of physical activity (PA; Friedenreich et al., 2021). Specifically, there is "strong" evidence that PA reduces the risk of bladder, breast, colon, endometrial, esophageal adenocarcinoma, and gastric cancers. As a result, public health agencies (e.g., Public Health Agency of Canada) promote PA as an important part of a healthy lifestyle and note that regular PA can help to reduce the risk of premature death and chronic diseases including breast cancer. The Canadian Society for Exercise Physiology (CSEP; https://csepguidelines.ca/guidelines/adults-18-64/) published recommendations for adults (aged 18-64) that include: (a) performing at least 150 minutes of moderate-to-vigorous intensity PA each week (i.e., activities that get your heart beating faster), (b) performing muscle strengthening activities at least twice a week, (c) limiting time spent sitting or laying down to 8 hours or less a day, and (d) achieving good quality and consistent sleep (i.e., 7 to 9 hours, with consistent bed and wake-up times).

Efforts to promote PA in adults at higher-than-average risk for breast cancer (reflected by their enrollment in the Ontario Breast Screening Program), are critical to reduce their risk of breast cancer. Despite the effectiveness of PA recommendations delivered through health care providers (HCPs), most individuals do not receive them during routine care as HCPs report barriers to promoting PA (e.g., inadequate training, lack of time/knowledge; Hébert et al., 2012). Research needs to focus on developing sustainable interventions that can be implemented broadly using distance-based approaches and available infrastructure (e.g., patient registries) without burdening HCPs to increase the consistency with which PA is promoted to adults at higher-than-average risk for breast cancer. Unlike self-guided PA interventions, supervised face-to-face PA interventions can be costly, unsustainable, and have limited ability to reach individuals unable (or unwilling) to travel to a facility where interventions are delivered (Haines et al., 2010; Ormel et al., 2018; Sevick et al., 2000). Thus, online interventions should be explored as a means to expand support to adults at higher-than-average risk for breast cancer, as a complement to offering PA recommendations. When self-guided, these interventions are easily scalable at a relatively low marginal cost per additional participant, accessible, self-paced, and available around the clock. Accordingly, they are frequently valued for their accessibility and convenience. Additionally, as interventions incorporating behaviour change techniques, such as goal setting and problem-solving, show greater sustained PA levels post-intervention, it is critical to embed those evidence-based techniques and PA materials (e.g., printed materials, logbook, webinars and education sessions) into online interventions if they are to be effective (Brunet et al., 2020).

Accordingly, this team of researchers and HCPs have partnered to develop and evaluate an intervention comprising of a copy of PA recommendations for adults (18-64 years) plus a motivation package (intervention arm) that can be implemented using a distance-based approach and sustained in the current healthcare system without burdening HCPs. This study aims to test the following hypothesis: the effects of the intervention on PA (primary outcome), quality of life (QoL) (secondary outcome), and body mass index (BMI; secondary outcome) in adults at high-risk of breast cancer will be greater in comparison to standard care plus a copy of PA recommendations for adults (control arm).

Inclusion Criteria:

• English- and French-speaking adults enrolled in the Ontario Breast Screening Program;

• Aged 30-69 years;

• Assigned female sex at birth;

• Be at high risk for breast cancer as identified through Category A or B, after genetic assessment: (a) Category A individuals meet ≥1 of the following criteria: (i) known carrier of a gene mutation (e.g., BRCA1, BRCA2), (ii) first degree relative of a carrier of a gene mutation (e.g., BRCA1, BRCA2), received genetic counselling but declined genetic testing, (iii) previously assessed as having ≥25% lifetime risk of breast cancer on basis of family history, or (iv) received chest radiation before age 30 and ≥ 8 years previously.

  (b) Category B individuals meet ≥1 of the following criteria: (i) first degree relative of a carrier of a gene mutation (e.g., BRCA1, BRCA2), has not had genetic counselling or testing, (ii) a personal or family history of ≥1 of the following: ≥2 cases of breast cancer and/or ovarian cancer in closely related blood relatives, bilateral breast cancer, both breast cancer and ovarian cancer in the same individual, breast cancer at age ≤35 years, invasive serous ovarian cancer, breast cancer and/or ovarian cancer in Ashkenazi Jewish families, an identified gene mutation (e.g., BRCA1, BRCA2) in any blood relative, male breast cancer.

Exclusion Criteria:

Individuals self-reporting

• >150 minutes of moderate-to-vigorous intensity physical activity in the past week;
• no access to an internet connected device;
• a condition preventing physical activity (e.g., uncontrolled hypertension)

The randomization will be concealed to the investigators throughout the trial; the investigators will not take part in the assessments or intervention delivery. The randomization will be concealed to study staff and participants until informed consent and baseline data are obtained. Study staff will be unblinded to group allocation upon randomization to enable delivery of the intervention arm and control arm corresponding materials, whereas the randomization will remain concealed to participants. To support blinding, all participants will be informed they are being enrolled in a study investigating ways to promote PA and will be kept blind to the fact that the intervention arm receives more materials than the control arm, and thus all (including participants allocated to the control arm) will receive materials (i.e., a copy of PA recommendations). Moreover, we do not anticipate participants to have contact with participants of the other arm.