Rationale: Breast cancer is among the most common malignancies in women, and metastasis significantly impacts survival and quality of life. Although many patients remain disease-free in the early years after surgery and adjuvant therapy, occult metastasis remains a major clinical concern. While bone, lung, and liver are common metastatic sites, gastrointestinal involvement is rare and often overlooked. Recent evidence suggests that late-stage occult metastasis can develop even after long disease-free intervals. Early detection is vital for optimizing treatment and improving prognosis. Therefore, gastrointestinal symptoms such as abdominal pain, altered bowel habits, or unexplained weight loss in breast cancer patients warrant prompt imaging and endoscopic evaluation. Patient concerns: This case report describes a 49-year-old woman with invasive lobular breast carcinoma who, after nearly 11 years of recurrence-free survival, presented with constipation and weight loss. Imaging and endoscopy revealed gastric and rectal metastases, underscoring the risk of occult metastasis in breast cancer. This case highlights the importance of considering age and treatment history when developing personalized management strategies and emphasizes early detection and intervention to improve outcomes and quality of life. Diagnoses: Computed tomography revealed thickening of the gastric antrum and rectal wall, resulting in luminal narrowing. A comprehensive flexible colonoscopy was performed, and biopsy of the colonic tissue for pathological examination indicated metastatic tumors in the rectal mucosa originating from breast cancer as well as metastatic lobular carcinoma in the stomach. Interventions: The patient is currently receiving a chemotherapy regimen of gemcitabine 1.4 g and carboplatin (500 mg). Outcomes: The patient is currently in the chemotherapy phase, and close monitoring of the condition is being conducted during treatment. Lessons: For patients with a history of breast cancer, the emergence of new gastrointestinal symptoms or a diagnosis of primary gastric or colorectal cancer should raise suspicion metastatic breast cancer. During the biopsy process, a comprehensive evaluation of histopathological and immunohistochemical analyses is necessary, and these results should be compared with those of primary breast cancer to ensure an accurate diagnosis.

The aim of this study was to apply a 2-sample Mendelian randomization approach, uncovering the causal link between artificial sweetener (AS) intake in cereals, coffee and tea and cancer. For this purpose, the research team obtained and utilized comprehensive data from published genome-wide association studies and selected genetic variants associated with AS as instrumental variables. Through 5 analytical techniques such as inverse variance weighting, MR-Egger, weighted median, simple multiple, and weighted multiple. In this study, the potential risk associations between AS and 15 cancers were comprehensively evaluated, and sensitivity analyses were used to assess the robustness of the results. Statistical results showed that there were causal associations between AS and breast cancer, oral cancer, esophageal cancer, gastric cancer, colorectal cancer, prostate cancer, ovarian cancer, kidney cancer, and lung cancer (inverse variance weighting method: P < .05). AS was a protective factor for breast cancer, gastric cancer, colorectal cancer, prostate cancer, and kidney cancer, and reduced their incidence. AS is a risk factor for oral cancer, esophageal cancer, ovarian cancer, and lung cancer, which increases the probability of occurrence. Sensitivity analysis showed that there was no significant heterogeneity or pleiotropy, and the results were relatively stable. AS intake was associated with a reduced risk of breast, stomach, colorectal, prostate, and kidney cancers; AS intake was associated with an increased risk of oral, esophageal, ovarian, and lung cancers.