Cancer survivors often experience psychological and interpersonal difficulties after diagnosis, in addition to physical problems [1]. Some patients are diagnosed with depression [2] and experience PTSD [3]. Simultaneously, some also experience positive personal changes [4, 5]. It is called posttraumatic growth (PTG) that is defined as positive changes that may occur as a result of a psychological struggle with a highly stressful life event [6]. Generally, PTG consists of five areas: New Possibilities (experiencing as developing a new path or opportunities), Appreciation of Life (experiencing greater appreciation for each day and for the value of life), Relating to Others (positive changes in interpersonal relationships), Existential and Spiritual Change (better understanding of spirituality or religious faith), and Personal Strength (increased self-reliance or greater sense of personal strength) [6,7,8]. These areas have been quantitatively and qualitatively identified [9, 10]. Related studies on cancer patients have been growing [5, 11], showing that hope, optimism, spirituality, and meaning are factors that contribute to the promotion of PTG [5]. In recent years, PTG trajectories have been reported in cancer survivors [12,13,14]. Some studies have reported patterns of high or low levels that remain unchanged, whereas others have reported increased or decreased the levels.

The palliation of psychosocial distress in patients with cancer has been emphasized, and a variety of psychosocial support services have become available (e.g., psycho-oncology departments and group therapy). However, few cancer patients use such services, even when they feel severe distress [15, 16]. Help-seeking behavior (HSB) is defined as problem-focused, planned behavior, involving interpersonal interactions with a selected healthcare professional [17]. The number of studies on HSB has also been gradually increasing, and factors contributing to the use of psychosocial support services among patients with cancer include the perceived need for psychosocial services and support, environmental conditions, physical problems, and psychological distress [11, 16, 18,19,20].

The commonality and complementary relationships between PTG and HSB have been highlighted theoretically in terms of culture, such as the positive psychology movement, subjective norms, and personalities at the individual level [11]. Both concepts originated and were refined primarily in the Western cultures. Therefore, people who would seem to fit Western cultural values may be more likely to report PTG and engage in HSB more easily. Meanwhile, we assume that it is difficult for people associated with a culture that is very different from Western values, such as the traditional Japanese culture, to experience both PTG and HSB. For example, previous studies have shown that PTG levels are lower in Japanese samples than in their American counterparts [7, 21]. Other studies have shown that the structure of factors of the Posttraumatic Growth Inventory (PTGI) for Japanese samples was different from the original [22] and that the expansion of the PTGI, the PTGI-X [23], was developed to specifically expand the Spiritual Change of the existing PTGI. As for HSB, its use is approximately 10–15% in Japan [15, 24, 25], compared to approximately 30% in patients with cancer in Western countries [26, 27]. Hence, we hypothesized that people who are more likely to experience PTG are also more likely to demonstrate HSB and that the opposite is also considered to be valid.

We hypothesized that experiencing HSB, that is, using psychosocial support services, would result in a higher level of PTG. Some aspects of psychotherapy techniques may promote PTG. Providers of psychosocial support services, psychiatrists, clinical psychologists, and social workers may play the role of expert companions who are well-trained professionals with humble attitudes and can help facilitate PTG [28]. When using psychosocial support services, individuals are required to disclose themselves to others. Increased social support was positively associated with PTG, supporting the notion that social support promotes PTG by enabling the disclosure of a highly stressful event [29]. One article mentioned the elements of psychotherapeutic or psychoeducational interventions for PTG, such as cognitive-behavioral, interpersonal, existential, narrative, and emotion regulation [30]. Additionally, studies examining whether psychosocial interventions, not limited to patients with cancer, can increase PTG levels, have received much attention. One meta-analytical study suggested that current interventions including written/spoken, cognitive-behavioral therapy modestly increase PTG, although the results need to be replicated because of the small number of eligible studies and various types of interventions [31]. Studies have also examined the effects of psychosocial interventions on PTG among patients with cancer. Some studies have shown that those who participated in a group intervention, one was a specific to promoting PTG, overall reported a higher level of PTG [32, 33]. Similarly, a recent meta-analysis focusing on patients with cancer showed that psychosocial interventions including supportive group psychotherapy and multiple health behavior change interventions increased PTG [34].

We also hypothesized that PTG experience would lead to HSB, although there is little evidence thus far as most studies have assumed PTG as an outcome. However, people who have experienced trauma and subsequent emotional struggles may have a sense of growth in their relationships, which in turn should help them be more willing to count on others in times of trouble, since it is a domain of PTG—Relating to Others [6, 22]. Talking to others and telling others about oneself are essential for HSB to psychosocial support services. Therefore, it can be assumed that those who have experienced PTG are less likely reserved to seeking help afterwards. One cancer patient who participated in psychosocial support services reported that one of the reasons for participating was because she could not do anything about her anxiety by herself and became to think that it might be fine to talk to someone to get some relief [35]. Additionally, according to one study [8], there may be a common between the three constituent themes (New Possibilities, Appreciation of Life, and Personal Strength), that is, having survived the traumatic event, people felt better at coping with future challenging situations. For example, as these components increase, they may engage in HSB to psychosocial support services as a coping such challenging situations.

We hypothesized that HSB and PTG would be positively associated with each other, as they may have a complementary relationship. This study aimed to examine this relationship using a longitudinal research design among patients with cancer.