In patients with breast cancer, higher levels of social support have been linked to positive outcomes, such as improved overall health status (Ganz et al., 2003), higher quality of life (Hoyer et al., 2011), and better adjustment to a cancer diagnosis (Helgeson & Cohen, 1996), as well as fewer psychosocial problems (Patten, Williams, Lavorato, & Bulloch, 2010; Helgeson, Snyder, & Seltman, 2004; Simpson, Carlson, Beck, & Patten, 2002). High social support is associated with lower risk of recurrence (Epplein et al., 2011) and longer survival (Chou, Stewart, Wild, & Bloom, 2010; Epplein et al., 2011). In patients with breast cancer, psychosocial variables such as perceived social support are often more strongly correlated with psychosocial distress than clinical variables related to disease and treatment (Andreau et al., 2011; Helgeson, Snyder, & Seltman, 2004; Schmidt & Andrykowski, 2004). The construct of social support has been measured in a variety of ways (e.g., as perceived availability of support, social network size, and actual receipt of certain types of support), and these different measures can be poorly correlated with each other (Mickelson & Kubzansky, 2003; Uchino, 2009). The current study focuses on perceived social support, which has been strongly linked to positive psychosocial and health outcomes (Uchino, 2009). Previous studies have identified a variety of demographic and psychosocial predictors of perceived social support including age (Sammarco, 2009; Schroevers, Helgeson, Sanderman, & Ranchor, 2010) and income (Mickelson & Kubzansky, 2003). Findings on race have been mixed, with some researchers finding that social support differs by race (Lincoln, Chatters, & Taylor, 2003) and others finding that racial differences in social support were accounted for by income and education (Mickelson & Kubzansky, 2003). In addition, psychological symptoms and social support have been closely linked, with some researchers finding that low social support is a strong predictor of future depression (Patten, Williams, Lavorato, & Bulloch, 2010) and others finding that more severe psychological symptoms are a strong predictor of lower future social support (Simpson, Carlson, Beck, & Patten, 2002). Previous research also has indicated that perceived social support in patients with breast cancer tends to decrease over time (Den Oudsten, Van Heck, Van der Steeg, Roukema, & DeVries, 2010; Courtens, Stevens, Crebolder, & Philipsen, 1996; Bloom & Kessler, 1994; Levy et al., 1992). The question remains whether such decreases in perceived social support are of concern. It is plausible that social support might be transiently higher in breast cancer patients at the time of initial detection and treatment (e.g., as friends and relatives rally to support the patient), resulting in perceived social support that is higher than that of controls (Schroevers, Ranchor, & Sanderman, 2003) but that support would decline over time. This decline in social support might leave breast cancer patients with similar quality of life to controls many years after cancer is detected (e.g., Helgeson & Tomich, 2005). However, it is also possible that even years after detection and initial treatment, breast cancer survivors need more social support than women without breast cancer. Although cross-sectional findings about perceived social support are generally consistent with the conclusion that more perceived social support is associated with better outcomes, some researchers have concluded that women with breast cancer both need and seek less support in the years after their diagnosis (Danhauer, Crawford, Farmer, & Avis, 2009; Badger, Braden, Longman, & Mishel, 1999), which might suggest that decreases in social support are unrelated to decreases in functioning and quality of life. The available literature has not, to our knowledge, considered that perceived social support may have a trajectory over time. That is, at any given time point, a person’s level of perceived social support may be a combination of her long-term tendency toward a certain average level of perceived social support as well as her more recent downward or upward trajectory of support, if any. A level of social support at one time may be a point on a line (trajectory), which may or may not be stable. Measurement of perceived social support at one or two time points, as is often done, cannot distinguish between these features of the construct. It is possible that many years after diagnosis, perceived social support reported by patients and controls does not differ, whereas the slope that brought patients to that point could be quite different from the slope shown by controls. Furthermore, it could be that patients’ slope predicts future negative outcomes that are independent of their current level of perceived social support. A steeper drop in support might be more important than the level of support at any given point. Examination of the social support trajectory can be undertaken using a latent trajectory model, which requires at least three waves of data and allows researchers to distinguish between systematic change in a construct over time (i.e., the slope) and general tendencies toward a certain level on a construct (i.e., the intercept, which is typically expressed in terms of the participant’s starting point) (Curran & Hussong, 2003). We propose that a clear understanding of how perceived social support changes for women with breast cancer is only possible through separating and examining these two parts of the construct of social support. Similarly, we propose that it is particularly important to understand what predicts change in perceived social support for breast cancer patients over and above their general tendencies for perceived support. We also contend that longitudinal changes in social support in patients with breast cancer must be analyzed in conjunction with data from same-age women without breast cancer in order to determine which predictors are specific to women with breast cancer. We used longitudinal data from a cohort of 1096 early-stage patients with breast cancer and age-matched controls to analyze the degree of change (slope) and the starting point level (intercept) of perceived social support measured four times over the course of two years. Quality of life research using similar methods has analyzed breast cancer patients as a heterogeneous group with different trajectories of depressive symptoms (Helgeson, Snyder, & Seltman, 2004; Dunn et al., 2011). However, rather than attempt to find empirically derived groups of patients, we used latent trajectory modeling (Curran & Hussong, 2003) to examine predictors of women’s social support trajectories. A latent trajectory model can be used to derive the estimated underlying trajectory of change in longitudinal data collected over several time points (Curran & Hussong, 2003). Including age-matched controls helped us determine whether slope and intercept of social support differed for breast cancer patients compared to controls, as well as which psychosocial, demographic, and clinical variables contribute to social support slope and intercept. We tested four hypotheses: Hypothesis 1: Social support is higher in patients than controls at baseline and decreases over time in patients but not controls. Hypothesis 2: Predictors of slope and intercept of social support differ from each other, and they differ between patients and controls. Because this is, to our knowledge, the first analysis of change in social support to examine slope and intercept separately, we expected that some predictors for slope might differ from predictors previously noted in the literature; thus we did not predict in which direction variables might influence social support. Hypothesis 3: Decrease in social support among patients is related to poorer psychosocial adjustment, as measured by higher levels of depressive symptoms. Hypothesis 4: Predictors of social support slope in patients exert indirect effects on depressive symptom severity through the slope of social support.