Advances in diagnosis and therapeutic technologies have brought increased life expectancy for most cancer survivors[10]. As a “side effect,” it also has increased the risk of SPMs. Approximately 5.78%-6.4% of cancer patients have a history of multiple cancers, and the rate is uprising. Most CC patients are unconcerned about SPMs and only undergo further examination after symptoms are obvious. Consequently, the survival rate decreased significantly[6]. It is meaningful to timely assess the risk probability of SPMs in CC survivors and the survival probability of CCSPM patients to get a prolonged life span.
In this study, 86.39% of CCSPMs were diagnosed five years later since CC onset. Female genital organs are the most common location of SPMs in CC patients. It is attributable to solid location relationships and shared risk factors, including HPV infection and smoking. CC survivors tend to repeat pelvic/abdomen computed tomography to measure treatment response and post-treatment surveillance[12]. It leads to an incidental finding of SPMs located in the gynecologic system. CC survivors with older age, married, Black population, lower grade, and earlier clinical stages were more likely to have SPMs. Histology grade, clinical stage, and treatment(surgery, chemotherapy, and radiotherapy) were the independent factors in predicting the occurrence probability and prognosis of CCSPMs. The diagnostic and prognostic nomograms demonstrated perfect consistency and discriminative ability between the anticipated risks and observed results. Our nomograms had potential clinical utility for future clinical practice.
Understanding SPMs' locations and interval time trends are essential for screening recommendations for CC survivors. Our data showed that the top three SPMs sites were female genital tracts, lungs, and breasts, which accounted for over 50% of all SPMs. Each SPM has specific mean interval times. The pelvic MRI was recommended around 91 months in the prevention of female system tumors. The molybdenum target was also suggested around 127 months to prevent breast cancer. Chest CT should be performed at about 174 months to detect lung cancer. Based on the occurrence trends of different types of SPMs for CC survivors, we could make up a focused follow-up strategy with a better economic risk-benefit ratio. The five years is widely acknowledged as the cut-off point to distinguish the high and low rates of potential CC recurrence and metastasis.[13] However, it doesn't mean CC survivors are "safe" after five years. CC survivors could still acquire SPMs in their lifetime since more than 80% CCSPMs occurred five years later in our study. We suggest CC survivors still need careful, long-term follow-up strategies for SPMs prevention.
On the other hand, although not available in the SEER dataset, the influence of shared risk factors for SPMs should be carefully weighted. HPV infection, tobacco use, diet, reproductive factor, and hormones have been well-proven to be associated with CC carcinogenesis[14]. In our study, CC patients' second tumor location was more frequent in female genital sites and digestive systems, which have been well proven to be associated with HPV infection[15].Tobacco is also regarded as a shared carcinogenic factor for tumors of the lung and bronchus, digestive system, female genital organs, and urinary system[16]. Properly handling these shared risk factors could help to reduce the incidence of SPMs.
Clinical stages (T, N, M, and FIGO stage) and treatment approaches (surgery, chemotherapy, and radiotherapy) were the most influential factors in the diagnostic nomogram. They could attribute or alleviate the susceptibility of SPMs. Previous studies have shown that early clinical stages contributed to the occurrence of SPMs, due to the longer lifespan compared to advanced clinical stages[17, 18]. Hysterectomy and oophorectomy directly reduce the incidence of future gynecologic cancers and indirectly decrease the occurrence of hormone-related breast cancers[19, 20].In contrast, platinum-based chemotherapy was positively associated with the event of SPMs in gastrointestinal cancer, testicular malignancy, and HPV-associated cancers[21]. In previous studies, radiotherapy was often recognized as a risk factor for SPMs.[22, 23] Interestingly, in our study, patients with a radiation history have a reduced risk of SPMs susceptibility. Previous studies[24–26]also showed patients with rectal and endometrial cancers had no increased risk of SPMs after pelvic irradiation. “incidental” radiation of the second pelvic tumors and only a tiny proportion of SPMs attributable to radiotherapy[24, 27]. Treatment approaches and clinical stages were also independent factors in our prognostic nomogram. Patients who refused treatment or with advanced clinical stage had poor 5-year overall survival. These results indicated that anti-CC therapy and earlier clinical stage not only could positively influence SPMs prognosis but also evoke the occurrence of SPMs to some extent. The diagnostic and prognostic nomograms may assist clinicians in timely evaluating the diagnosis and prognosis of CC patients with SPMs and optimize individualized treatment plans.
To our knowledge, this study is the first to identify the diagnostic and prognostic factors associated with SPMs among CC survivors in SEER. However, our study has certain limitations. First, the SEER database has no detailed information on shared risk factors, including HPV infection, smoking, diet, and hormones, so how these factors contribute to the development of SPMs needs further exploration. Second, since few CC survivors had SPMs in the thyroid, lymph nodes, and skin, we did not investigate their prognosis. Third, the study's statistical results may be biased because of many unknown (No/Unknow) variables in SEER.