A cancer diagnosis is a stressful life event that could lead to higher levels of psychological distress. As a result of its traumatic nature, cancer could trigger certain posttraumatic reactions. The most examined posttraumatic reactions in cancer are posttraumatic stress disorder (PTSD) as the negative changes and posttraumatic growth (PTG) as the positive changes. PTSD and PTG can coexist with each other and have some shared and different correlates. PTSD, PTG, their relationships and their correlates have mostly been studied in mixed samples of patients having cancer treatment and as well as cancer survivors. The present study explored PTSD, PTG, their correlates and their interconnection in separate samples of patients in active treatment (N = 181) and cancer survivors (N = 419). It examined various types of correlates such as sociodemographic (e.g., gender, age), cancer-related (e.g., relapse, late treatment impact), coping (e.g., anxious preoccupation, fighting spirit), emotional (e.g., pain, depression), personality factors (e.g., neuroticism, resilience), eudaimonic (e.g., meaningfulness), social (e.g., regular attendance of cancer support group) and spiritual (e.g., the practice of spirituality). In addition, network models of PTSD, PTG and PTSD-PTG were estimated and compared in both samples. There were different correlates of PTSD and PTG found in patients and survivors. From the network perspective, PTG and PTSD were linked in different patterns in both groups. These results highlight which correlates of posttraumatic reactions are important for patients in treatment and for cancer survivors. The results also depict which PTSD symptoms and PTG indicators are most important in the PTG-PTSD interconnection amongst patients and survivors.