Can Sex be A Predictor of Survival and Treatment Benet in T1-3N0M0 colorectal Cancer Patients? A Population-Based Analysis

Background: Our aim was to assess predictive effect of sex on survival and treatment benet of T1-3N0M0 CRC. Methods: This study population was assembled from the SEER dataset. Between 2004 and 2016, patients diagnosed with malignant primary CRC who underwent primary tumour resection were included. Results: First, we found that females had better OS than males and that sex could be an independent factor of survival in T1-3N0M0 colon cancer (regardless of right/left-sided tumour) and T1-2N0M0 rectal cancer (each HR<1, each P<0.05). In addition, though a signicant OS benet was not observed in T3N0M0 rectal cancer in the overall analysis (P=0.183), females beneted more than males among T3N0M0 rectal cancer patients who underwent postoperative chemotherapy (P<0.001). However, there was no signicant OS difference between male and femaleT3N0M0 rectal cancer patients among those who did not receive postoperative chemotherapy (P=0.634). In subgroup analyses of T3N0M0 patients, a similar tendency of survival and the effect of postoperative chemotherapy were observed regardless of whether preoperative radiotherapy was performed. Furthermore, we found that females had a survival benet over males at all ages, among patients of the white race and among T1-T3 adenocarcinoma CRC patients (each HR<1, each P<0.001). Conclusion: Sex was proven to be an independent prognostic factor in T1-3N0M0 colon cancer and T1-2N0M0 rectal cancer. Females are more likely to benet from postoperative chemotherapy than males with T3N0M0 rectal cancer. Our research suggests that sex could be considered a factor in practical clinical treatment and prognosis evaluation for T1-3N0M0 rectal cancer. HR, Hazard ratio; CI, Condence interval.


Introduction
Cancer is the main global public health problem and is also the second primary cause of death in the United States of America [1]. Colorectal cancer (CRC) is one of the most common malignant tumours in the United States. In the male population, CRC is the third most common cancer after prostate cancer and lung cancer, with an estimated 78,300 new cases (9% of all new cancers) in 2020. In the female population, CRC is the third most common cancer after breast cancer and lung cancer. It is estimated that there will be 69,650 new cases (8% of all new cancers) in 2020. CRC also has a high death rate. CRC is the third most common cause of cancer death in males, with a total of 28,630 deaths (9% of all cancers) expected in 2020. Likewise, CRC is the third most common cause of cancer death among females, with 24,570 deaths (9% of all cancers) expected in 2020. Although the morbidity and mortality of CRC rank third in both males and females in the estimated data, there are some differences between the sexes. In the vast majority of cancers, there are some differences between males and females in morbidity and prognosis, which is the reason why cancer data of males and females are separated.
The in uence of sex on CRC has also been a hot topic in recent years. Several studies have shown that sex is an independent prognostic factor for CRC and that females generally have longer survival times than males [2][3][4][5][6][7][8]. Compared to males of all ages, females are less likely to have CRC [9][10]. In fact, their risk is equivalent to that of males 4 to 8 years younger [11]. There are several probable explanations that sex differences in CRC extend to environmental in uence, tumour biology, and therapeutic response [12].
Hormones may be one reason. Postmenopausal hormone use has been linked to a 40% reduction in CRC in the Women's Health Initiative trial [13]. The link between hormone replacement therapy and colon cancer prevention is the same as in former reports [14][15].The biological features of tumours may be different between males and females. There is also evidence that women are more likely to develop rightsided colon cancer with microsatellite instability [16][17]. Furthermore, some reports suggest that females present at a more advanced stage of cancer [18] on average. All aforementioned differences should be taken into account as confounding factors.
Therefore, females are more often hormone carriers and more often have right-sided colon cancer and more advanced stages of cancer. We selected patients aged 60 years and over (menopause) and patients with stage T1-4N0M0 (early local tumours) for analysis after strati cation of the primary tumour site. Our aim was to assess the prognostic effect of sex on survival after removal of known confounding factors.

Patients
Between 2004 and 2016, patients diagnosed with malignant primary CRC were included in the study. The disease was de ned by International Classi cation of Diseases for Oncology, third edition (ICD-O-3) codes (18.0, 18.2-18.7, 19.9 and 20.9). All patients who were diagnosed with CRC at or above the age of 60 underwent primary tumour resection. The patients were excluded from this study population if they (1) died within 30 days after tumour resection; (2) had Tis, N1, N2 or M1 cancer; (3) had other cancers before; or (4) lacked records of pathological stage, follow-up or histological subtype. These cases were organized by SEER's coding schemes. On the basis of the primary location of the tumour, patients were divided into three groups. Right-sided colon cancers were de ned as those arising from the caecum (C18.0), ascending colon (C18.2), hepatic exure of the colon (C18.3) or transverse colon (C18.4); left-sided colon cancer was de ned as those arising from the splenic exure of colon (C18.5), descending colon (C18.6), and sigmoid colon (C18.7); rectum cancers were de ned as those developing from the rectosigmoid junction (C19.9) or rectum (C20.9).

Data Collection
This study population was assembled from the National Cancer Institute's Surveillance, Epidemiology, and End Results (SEER) Program. SEER data include cancer cases from different locations and sources across the United States. Only a limited number of registration agencies have been collected since 1973. The dataset continues to broaden by including more geographic areas and demographic groups. It cover approximately 28% of the U.S. population and includes data from various geographic areas, including incidence, prevalence, mortality, population-based variable quantities, main characteristics of the tumour, and other attributes. SEER * Stat software version 8.3.6 was used to gather the main data.

Statistical Analysis
The chi-square test was used to compare the baseline characteristics of males and females. Overall survival outcomes were estimated with the Kaplan-Meier (KM) method, and the differences between survival were compared by the log-rank test. Multivariable Cox regression was used to calculate hazard ratios (HRs) and 95% con dence intervals (CIs). All analyses were double-sided, and a P value lower than 0.05 was deemed statistically signi cant. All analyses were performed using the statistical software STATA® 8.0 (STATA Inc, College Station, TX).

Demographic characteristics of male and female CRC
We obtained a dataset that included 70,836 cases of CRC in males and 69,705 cases of CRC in females.
The characteristics of CRC and the chi-square test for comparison of male and female CRC are shown in Table 1. We found some signi cant differences in age, race, histological grade, chemotherapy, marital status, histology, radiation, pT category and primary site (each P < 0.001). Compared with males, females more often hadage ≥ 75 years (55.1% vs. 44%), right-sided colon cancer (56.8% vs. 45.4%), and pT2-4 cancer (75.5% vs. 72%). In uence of sex on OS in T any N 0 M 0 There was a signi cant difference in survival between males with CRC and females with CRC in the T1 category (P < 0.001, Fig. 1-A). There were similar signi cant differences in the T2 and T3 categories (P < 0.001, Fig. 1-B; P < 0.001, Fig. 1-C). In the T4 category, we discovered no difference in survival between male CRC and female CRC (P = 0.784, Fig. 1-D). In consideration of the above outcomes, we held T4 CRC out of our analyses. The multivariable Cox regression (Table 2) showed that sex was an independent prognostic factor (HR = 0.716; 95% CI = 0.703-0.730; P < 0.001). In uence of sex on OS after strati cation by T category and primary site T1 category In right-sided colon cancer, there was no signi cant difference in survival between male CRC and female CRC (P < 0.066, Fig. 2-A), but we discovered signi cant differences on multivariable Cox regression (Supplemental Table 1), and sex was shown to be an independent prognostic factor (HR = 0.739, 95% CI = 0.696-0.785, P < 0.001, Fig. 3). In left-sided colon and rectal cancer, there were signi cant differences in survival between male CRC and female CRC (P < 0.001, Fig. 2-B; P < 0.001, Fig. 2-C).We also saw the result upon multivariable Cox regression (Supplemental Table 1). Sex was also proven to be an independent prognostic factor in this analysis (HR = 0.730, 95% CI = 0.705-0.756, P < 0.001; HR = 0.688, 95%CI = 0.639-0.740, P < 0.001, Fig. 3).

T3 category
We saw signi cant differences in survival between male patients and female patients with right-sided colon or left-sided colon cancer (respectively, P < 0.001, Fig. 2-G; P < 0.001, Fig. 2-H). We discovered the same signi cant differences in multivariable Cox regression (Supplemental Table 3), which again showed that sex was an independent prognostic factor (HR = 0.721, 95% CI = 0.696-0.746, P < 0.001;HR = 0.708, 95% CI = 0.674-0.745, P < 0.001). In the rectum, there was no signi cant difference in survival between male CRC and female CRC (P = 0.183, Fig. 2-I). We did not perform multivariable Cox regression on these data. It is apparent that sex is not an independent prognostic factor in rectal cancer.
In uence of sex and postoperative chemotherapy on OS in rectum of T3 Taking all tumours of the T3 category ( Fig. 4-A), patients with postoperative chemotherapy had a better survival bene t than individuals without postoperative chemotherapy among females (P < 0.001) or males (P < 0.001). We also found that females had a better survival bene t than males in all tumours of the T3 category with postoperative chemotherapy (P < 0.001). There were no signi cant differences in survival between males and females without postoperative chemotherapy (P = 0.634).
For tumours with a postoperative pathological stage of T3N0M0, the preoperative clinical stage is often more advanced and may generally be locally advanced. These patients are also often treated with preoperative radiotherapy. Therefore, we performed a subgroup analysis for patients with and without preoperative radiotherapy.
Among patients with T3 tumours who underwent preoperative radiotherapy (Fig. 4-B), those who also underwent postoperative chemotherapy had a better survival bene t than individuals without postoperative chemotherapy in both the female (P = 0.001) and the male sex (P < 0.001). We found an apparent difference, though without statistical signi cance, in survival between males and females with postoperative chemotherapy (P = 0.069). There were no signi cant differences in survival between males and females without postoperative chemotherapy (P = 0.226).
Among patients with T3 tumours who underwent preoperative radiotherapy (Fig. 4-C), those who underwent postoperative chemotherapy had a better survival bene t than individuals without postoperative chemotherapy in both the female (P = 0.001) and the male sex (P < 0.001). We also found that females had a better survival bene t than males with postoperative chemotherapy (P < 0.001). There were no signi cant differences in survival between males and females without postoperative chemotherapy (P = 0.618).

Discussion
Cancer is a major global public health problem and is also the second primary cause of death in the United States [1]. There are many differences between males and females in morbidity, mortality, prognosis, and biological behaviour for most cancers. The sex differences in cancer survival have attracted great attention because they may be a signal of basic biological differences between males and females in cancer pathogenesis and treatment response, which can be incorporated into management strategies. Therefore, sex differences are an essential research direction in tumour research. Interestingly, females seem to have better outcomes in most tumours, such as low morbidity, low mortality, and better prognosis. Moreover, a systematic review indicated that female patients also often have a survival advantage over male patients in many cancers [19]. Among the sex differences in some cancer manifestations, researchers have found that some may be related to male occupational and environmental exposures [20]. Nevertheless, in many circumstances, despite the control of environmental and genetic factors, the sex differences found in many cancers remain unexplained [21][22]. Our study focussed on the prognostic impact of sex on early local CRC. CRC is one of the most common malignant tumours in the U.S. It is the third most common tumour in both male and female patients. The estimated new cases in 2020 will be 78,300 in males and 69,650 in females. Among all tumours, the mortality rate of CRC ranks third among males and females. The data for 2020 projected deaths are 28,630 male patients and 24,570 female patients. Although the morbidity and mortality of CRC rank third in both male and female patients, there are some differences in their morbidity, mortality and prognosis.
The in uence of sex on CRC has also been a hot topic in recent years. In 2001, a German study surveyed nearly 900 patients and concluded that being female was related to improved long-term survival in rectal cancer [6]. In 2003, a similar study evaluated 3,200 cases and found that females had a survival bene t in CRC [5]. More studies have indicated that sex is an independent prognostic factor in CRC, and females usually live longer than males [2][3][4][5][6][7][8]. Other studies indicated that females improved OS compared with males [3,5,[23][24]. Compared to males of all ages, females are less likely to have CRC [9][10]. In fact, their risk is equivalent to that of males 4 to 8 years younger [11]. Thus, the effect of sex on CRC is well recognized. Although a large number of studies have shown that the female prognosis is better than male prognosis in many cases, there were many confounding factors that resulted in the better outcomes of women than men in these studies.
Therefore, the purpose of our research is to see whether the female superiority over males remains after controlling for confounding factors. There are several explanations for the sex differences in CRC, including environmental in uence, tumour biology, and therapeutic response. First, hormones may be one reason. Postmenopausal hormone use has been linked to a 40% reduction in CRC in the Women's Health Initiative trial [13]. This link between hormone replacement therapy and colon cancer prevention is in line with former reports [14][15]. Therefore, we believe that oestrogen may be a confounding factor, so our study cohort included only menopausal women. Menopause is usually de ned as 12 months of amenorrhea in females over 45 years of age. It usually starts between 45 and 55 years of age, with an average age of 50.5 years [25]. However, there are women who go into menopause after age 55 [26]. Based on the above, we only selected patients aged 60 years and older to form our study cohort to ensure that all female patients were postmenopausal. Next, the biological features of tumours may be different between males and females. There is evidence that females are more likely to develop microsatelliteunstable phenotypes of right-sided tumours [7,27]. Furthermore, some reports suggest that females present at a more advanced stage of cancer [18]. Consequently, we selected early local CRC of stage T1-4N0M0 for analysis after strati cation of the primary tumour site. Some studies have shown that sex, age, and ethnicity play an important role in the OS of CRC patients. A review of the literature showed that we analysed the largest cohort of colorectal cancer patients, and sex and age had an important impact on the OS of CRC patients. Therefore, we also conducted a detailed analysis strati ed by both race and age.
In that analysis, we still found that females had better survival than males with T1-3N0M0 colon cancer and T1-2N0M0 rectal cancer after taking away the effects all known confounding factors. However, there was no difference in survival between sexes among T3N0M0 rectum cancer patients. For rectum tumours with a postoperative pathological stage of T3N0M0, the preoperative clinical stage is often more advanced and may generally be a locally advanced stage. These patients are often treated with preoperative neoadjuvant treatment. For rectum cancer of the pT3N0M0 stage, the recommendation of the NCCN guidelines [28] is adjuvant therapy or observation. Adjuvant therapy is often recommended for T3rectal cancer with prognostic risk factors. Therefore, we also performed a subgroup analysis of patients with and without preoperative radiotherapy. As a result, we found the bene ts of female sex among T3N0M0 rectum cancer patients who underwent postoperative chemotherapy, regardless of whether preoperative radiotherapy was performed. Moreover, the results indicate that the T3N0M0 rectum cancer patients who underwent postoperative chemotherapy had a survival bene t over individuals without postoperative chemotherapy, regardless of sex. Females more often have tumours with microsatellite instability. This reason, as suggested in many studies, could be that females bene t more from chemotherapy [17,29].However, all of these studies were con ned to more advanced CRC, and there are few studies about the in uence of sex on chemotherapy in early-stage tumours (T3N0M0). Although it is generally accepted that females have a better survival than males, we did not nd a survival bene t of females with T3colorectal cancer. A signi cant survival bene t was obtained in rectum cancer patients with postoperative chemotherapy, which also con rmed that women can bene t more from postoperative chemotherapy in early rectal cancer (T3N0M0).Therefore, in addition to the existence of risk factors, female sex can also be considered an indicator for postoperative chemotherapy in T3N0M0 rectum cancer.
Although this research is based on a large number of samples, our research should be interpreted on the background of some limitations, some of which are intrinsic in the design of retrospective studies. Our results may not be representative of young patients with colorectal cancer. To exclude the effects of oestrogen on the results, we included only colorectal cancer patients aged 60 years and older. Information on radiotherapy and chemotherapy was 'None/Unknown', so we cannot rule out that some of these people had undergone radiotherapy or chemotherapy. Many signi cant clinical factors, predictive and prognostic biomarkers (e.g., microsatellite instability status), and behavioural differences (e.g., smoking, alcohol, diet, exercise and physical activity) were not available. In addition, there was no information in the SEER database about menopausal status or use of hormone therapy. Thus, there may have been some postmenopausal patients who were still taking oestrogen. Despite these limitations, our large-scale population-based research may make our conclusions more persuasive.
In conclusion, we found that females have a survival bene t over males among patients with T1-3N0M0 colon cancer and T1-2N0M0 rectal cancer. Sex was also proven to be an independent prognostic factor in T1-3N0M0 colon cancer and T1-2N0M0 rectal cancer. Females are more likely to bene t from postoperative adjuvant chemotherapy than males with T3N0M0 rectal cancer. Our research suggests that sex could be considered a factor in practical clinical treatment and prognosis evaluation for stage T1-3N0M0 rectal cancer. Especially in clinical decision-making on postoperative adjuvant therapy for T3N0M0 rectal cancer, female sex can also be considered an indicator for postoperative adjuvant therapy.

Conclusion
Perspectives and signi cance In summary, based on the SEER database, we investigated predictive effect of sex on survival and treatment bene t of T1-3N0M0 CRC. First, we found that females had better OS than males and that sex could be an independent factor of survival in T1-3N0M0 colon cancer (regardless of right/left-sided tumour) and T1-2N0M0 rectal cancer. In addition, though a signi cant OS bene t was not observed in T3N0M0 rectal cancer in the overall analysis (P=0.183), females bene ted more than males among T3N0M0 rectal cancer patients who underwent postoperative chemotherapy (P<0.001). In brief Females are more likely to bene t from postoperative chemotherapy than males. In the clinical environment, sex could be considered a factor in practical clinical treatment and prognosis evaluation for T1-3N0M0 rectal cancer. Bin Ma contributed to the conception of the study; Yongmin Li contributed signi cantly to analysis and manuscript preparation; Bin Ma performed the data analyses and wrote the manuscript; Qingkai Meng helped perform the analysis with constructive discussions.
observed in T3N0M0 rectal cancer in the overall analysis (P = 0.183), females bene ted more than males among T3N0M0 rectal cancer patients who underwent postoperative chemotherapy (P < 0.001). In brief,Females are more likely to bene t from postoperative chemotherapy than males. In the clinical environment, sex could be considered a factor in practical clinical treatment and prognosis evaluation for T1-3N0M0 rectal cancer. Figure 1 Kaplan