Objective: to understand the experience of families living with pregnancy-associated cancer. Method: grounded theory with symbolic interactionism as a theoretical reference. Twelve families with a woman diagnosed with pregnancy-associated cancer participated in the study. Data were collected by identification form, genogram and interview, between March 2018 and March 2019, and the analysis followed the stages of substantive and theoretical coding. Results: the constant comparative analysis of the data developed the substantive theory "Living between weaknesses and motivations: experiences of families with pregnancy-associated cancer" explaining the experience with the central concept "Living between losses that weaken and the arrival of the child who strengthens", which represents the symbolic actions and strategies of the family that perceives itself in a condition of duality. Conclusion: throughout the experience, the family moves from a condition in which illness is identified as a difficulty for the experience of pregnancy and birth to another in which pregnancy and birth are seen as motivators for cancer treatment.