Colorectal Cancer: Correlating the Role of Peritoneal Fluid Cytology to Tumor Biology and Stage: A Prospective Study from Pakistan.

Background: Colorectal cancer (CRC) is among the most common carcinomas globally and a leading cause of cancer-related mortality. In Pakistan, it is the fifth most diagnosed malignancy and the fourth leading cause of cancer death. A significant number of patients present at advanced stages, limiting curative treatment options. Peritoneal metastasis is a recognized route of disease spread in CRC, following hepatic and pulmonary metastasis. While peritoneal washing cytology (PWC) is an established prognostic tool in gastric and gynecological cancers, its role in CRC remains unclear and underutilized. Objective: This study aimed to evaluate the association of peritoneal fluid cytology with tumor stage, histological subtype, and tumor differentiation in patients with CRC in a Pakistani population, with the secondary goal of evaluating its prognostic significance and potential therapeutic implications. Materials and methods: We conducted a prospective observational study at the GI and HPB Department of SIUT Hospital, Karachi, from July to September 2025. A total of 83 patients aged 18-80 years with biopsy-proven colorectal adenocarcinoma, meeting specific inclusion criteria, were enrolled. Peritoneal lavage was performed intraoperatively before tumor manipulation, and cytological analysis of the fluid was conducted using standardized techniques. Cytology was deemed positive if malignant or atypical cells were identified. Statistical analysis was performed using SPSS version 26, with significance set at Results: Among the 83 patients, 71.1% were male, with a mean age of 41.3 ± 14.9 years. Rectal cancer was more prevalent (69.9%) compared to colonic cancer (28.8%). Signet-ring cell carcinoma was the most common histological subtype, found in 60.9% of patients, followed by mucinous adenocarcinoma (39.1%). Poorly differentiated tumors were observed in 43.3% of cases. Peritoneal cytology was positive in 14 patients (16.9%). Positive cytology was significantly associated with signet-ring cell carcinoma ( Conclusion: Peritoneal fluid cytology was found to correlate with aggressive tumor histology and advanced staging in CRC, suggesting its potential as a prognostic marker. While not currently part of routine staging protocols for CRC, positive peritoneal cytology could identify patients at higher risk for recurrence and poor outcomes. These patients may benefit from intensified treatment approaches, including consideration for cytoreductive surgery (CRS) and hyperthermic intraperitoneal chemotherapy (HIPEC), as well as closer postoperative surveillance. Larger multicenter studies with long-term follow-up are warranted to confirm these findings and to explore the therapeutic implications of cytology-positive status in CRC. How to cite this article: Hasan SR, Muhammad S, Khan S,