Improvements in healthcare services and living conditions are leading to a rapid increase in the elderly population worldwide. As life expectancy increases, the incidence of colorectal cancer in the patients of advanced age is also increasing, leading to a rise in the number of older adults requiring surgical treatments (1). Because surgery is the only curative treatment for colorectal cancer, even in the elderly patient, surgical resection is being actively performed (2). As the advanced age population is expected to grow continuously, and age is a significant risk factor for colorectal cancer, the diagnosis and treatment of colorectal cancer in this age are anticipated to further increase (3).

While the health of the older adults has improved significantly, it is essential to acknowledge that despite these advancements, age-related physiological changes lead to a reduced capacity to tolerate stress. Factors such as diminished immune function and impaired tissue healing contribute to this vulnerability compared to younger individuals (4). Elderly patients commonly present with multiple comorbidities including hypertension, diabetes, cardiovascular disease, pulmonary disease, and renal dysfunction, which are more common in this age group and contribute to increased surgical risk. Hence, these patients frequently face elevated postoperative risks and have a higher susceptibility to infectious complications, which can lead to potentially life-threatening outcomes (5).

In recent years, there has been a growing body of research exploring the optimal strategies for minimizing postoperative complications in elderly patients. By extending the duration of postoperative antibiotic prophylaxis in elderly patients, who appears to have the potential to reduce postoperative complications. This study aimed to evaluate whether prolonged postoperative antibiotics administration is associated with improved postoperative complications in elderly (≥70 aged) patients undergoing curative colorectal cancer surgery.

According to the World Health Organization GLOBOCAN database, colorectal cancer ranks as the third most commonly diagnosed cancer in males and the second most commonly diagnosed in females globally, with expectations of continued increase (6). Similarly, at the present institution, the number of colorectal cancer surgeries in patients over 70 years of age is gradually increasing (Figure 2). Elderly patients exhibited a heightened incidence of postoperative complications, notably infection-related issues including surgical site infections, urinary tract infections, and respiratory infections (7, 8). As a result, this leads to an increase in both the length of hospital stay and admission rate to intensive care units, along with higher rates of morbidity and mortality (9, 10). While complication prevention is important for all age groups, tailored strategies for complication prevention are necessary considering the specificity of the elderly population (11–13). Recently, in colorectal surgery, the combination of oral antibiotics with mechanical bowel preparation is recommended, given its advantages in terms of reducing anastomotic leakage, morbidity, mortality, and healthcare costs (14). Conversely, it has been established that the routine use of antibiotics for postoperative days does not provide any additional benefits (15). However, these studies were conducted on relatively younger populations, and the benefits of postoperative antibiotic use in the elderly groups have not been definitively established.

Anastomotic leakage after colorectal surgery is devastating complication resulting in significantly increased morbidity, mortality, and medical expense. The rate of anastomotic leakage, approximately 10 percent, varies based on the location of the anastomosis and differs among studies due to variations in its definition (16, 17). The human intestinal microbiome is believed to intricately contribute to the pathogenesis of physical conditions such as obesity, gastrointestinal malignancies, and Crohn's disease (18, 19). However, its impact on various diseases remains largely undiscovered. The healing and disruption of anastomosis after colorectal resection is one of the relatively unexplored area where intraluminal microbes are anticipated to play a crucial role.

The first investigation that evaluates effect of the microbiome on colonic anastomosis administered antibiotics directly to the anastomotic site via an indwelling catheter (20). The study group demonstrated complete anastomotic healing, while the control group which administered saline without antibiotics developed leakage, peritonitis, and death. Another similar study in the rats exhibited the healing effect of the non-absorbable oral antibiotics on colonic anastomosis (21). In applying these findings to a prospective, randomized, double-blind and placebo-controlled clinical multicenter trial, the patients with oral decontamination, from preoperative day to postoperative day 7, after total gastrectomy for gastric cancer showed lower mortality and fewer anastomotic leakage compared to the placebo group (22–24). The surgical group applied this protocol to colorectal surgery (25). The treatment group was administered oral antibiotics starting the day before surgery until postoperative day 7, demonstrating a lower rate of anastomotic leakage and infectious complications compared to the placebo group. In present study, the patients were administered systemic antibiotics instead of oral antibiotics and this is significant because, while the incidence rate of anastomotic leakage is generally known to be around 10%, in this study, the POD#1 group exhibited a lower incidence rate of 4.2%, and the POD#3 group showed an even lower rate of 1.3%.

All surgeries conducted under general anesthesia carry the risk of developing postoperative pneumonia, which can lead to substantial morbidity and mortality. The incidence of postoperative pneumonia has been reported to range from 2.2% to 13% (26), but more prevalent in the elderly patients with old age itself being a risk factor (27). General anesthesia and surgery, along with consequent atelectasis, alter lung mechanics and breathing patterns, thereby making the lung defense system more susceptible to infection (28, 29). Additionally, the incidence of postoperative pneumonia tends to be higher in patients with atelectasis, which occurs more frequently in old ages (30–32). Although the use of postoperative antibiotics to prevent or reduce the incidence of postoperative pneumonia haven't been established, this study is significant in that the incidence of postoperative pneumonia in the POD#3 group was 0% compared to 5.6% in the POD#1 group. Given that postoperative pneumonia is more fatal in the elderly, it is necessary to consider additional antibiotic use beyond conventional practice.

In this retrospective cohort study of 292 patients aged ≥70 years undergoing curative colorectal cancer surgery, prolonged postoperative antibiotic administration (≥3 days) was associated with a significantly lower rate of overall complications, infection-related complications, and postoperative antibiotic reuse compared with standard discontinuation on postoperative day 1. Notably, the POD#3 group demonstrated markedly reduced rates of anastomotic leakage and pneumonia, both of which are particularly detrimental in elderly and comorbid populations. Although our results differ from guideline recommendations, they should not be interpreted as evidence to change clinical practice. Instead, they highlight a potential gap in current evidence: the lack of prospective studies focusing on high-risk elderly surgical patients. The reduced rates of anastomotic leakage and pneumonia observed in our study may warrant further evaluation in controlled trials targeting this vulnerable population.

This study has several limitations. Its retrospective design introduces the potential for selection bias, and decisions regarding prolonged antibiotics were at the discretion of treating surgeons. Residual confounding may remain despite multivariate adjustment. Additionally, this is a single-center experience and may not be generalizable to other institutions with different perioperative protocols. Nevertheless, the consistent benefit observed across multiple clinically relevant outcomes suggests that postoperative antibiotic duration may merit further investigation in elderly colorectal cancer patients.

In conclusion, while prophylactic guidelines discourage extended postoperative antibiotics for the general population, the present study data indicate a possible role for selective use in order, high risk patients. Prospective randomized studies are needed to validate these findings and to better defined which elderly patients may benefit from prolonged postoperative prophylaxis.