Colorectal cancer is the third leading cause of cancer worldwide, accounting for a substantial number of tumor-related deaths. Recurrence occurs in roughly one-third of patients during the first two years after surgery.
Due to its direct examination of malignant cellular metabolism, PET/CT has been shown to have a crucial role in early diagnosis of post-therapeutic recurrence in patients with cancer colon.
It plays an important role in detecting metabolically active small LNs, local operative bed recurrence, small metastasis, early osseous deposits, and post-therapeutic evaluation of viable and non-viable malignant lesions (post chemotherapy and radiotherapy).
This study was conducted on 30 patients with age ranged from 36 to 77 years old with mean ± SD of 58.03 ± 12.34; they were 20 females (66.7%) and 10 males (33.3%).
Based on lesions analysis, the final diagnosis of local recurrence/spread in post-therapeutic cancer colon was visible in 18 cases (60.0 percent) of the patient group.
The study almost agreed with Mittal et al. , who found recurrences in 71 percent of post-operative CRC patients using PET/CT, but these findings differ from those of Hetta et al.  analyzed 60 instances and discovered that 22 cases (36.7 percent of the total evaluated cases) developed a local recurrence and 38 cases did not (63.3 percent percentage of the total studied cases). The study looked at the sensitivity, specificity, and accuracy of PET/CT in detecting local recurrence in colorectal cancer patients who had completed their treatment. The accuracy is 96.7 percent, with a sensitivity of 95.45 percent, a specificity of 97.36 percent, and a sensitivity of 95.45 percent.
In this study, the number of patients with local nodal involvement were 18 cases (60%). While 12 patients did not develop nodal metastatic deposits (40%).
The findings are consistent with those of O'Connor et al. , who found that on PET-CT, enlarged and non-enlarged FDG avid lymph nodes can be seen in the mesentery, indicating the existence of regional lymph node metastases; this is shown when patients with CRC are restaged. The study agreed because the research found that PET/CT was quite sensitive in detecting regional lymph nodes; however, this contradicts Kim et al. , who found that nodal 18F-FDG uptake findings were highly specific for LN metastatic status, but had a low sensitivity; this study's low sensitivity was attributed to the fact that the subsequent study excluded patients who had received neoadjuvant treatment, and they stated that if these advanced rectal cancer patients who had received neoadjuvant chemotherapy were included in the current study, the LN detectability of 18F-FDG PET/CT would be improved because the majority of these patients had shown high nodal 18F-FDG uptake.
The end diagnosis of distant metastases in post-therapeutic cancer colon was visible in 17 individuals (56.7%) of the patient group based on lesions investigation. Patients with hepatic metastatic deposits accounted for 12 instances (40%); those with pulmonary nodular deposits accounted for 8 cases (26.7%); those with osseous deposits accounted for 6 cases (20%); and those with peritoneal deposits accounted for four cases (40%).
PET/CT was therefore useful in detecting hepatic and extrahepatic metastases.
The findings are consistent with those of Kijima et al. , who found that FDG-PET and PET/CT have high accuracy for the detection and staging of liver lesions in CRC patients, with a combined sensitivity and specificity of 93 percent, and Zhang et al. , who found that PET/CT had better sensitivity and specificity (87–100 percent and 90–98 percent, respectively) for the detection and staging of liver lesions in CRC patients.
In this study, females had a statistically significant higher rate of PET-CT detection of recurrence, local spread, and local lymph nodes than males, with p-values of 0.018, 0.018, and 0.002, respectively, whereas there was no statistically significant relation between gender of the studied patients and the other findings, which could be due to small sample size.
In this study There was statistically significant increase in the PET-CT false negative rate in mucinous group than adenocarcinoma group with p-value < 0.001 while no statistically significant relation found between pathological results and the other findings.
The findings were consistent with those of Whiteford et al.  and Borasio et al. , who found that mucinous adenocarcinoma was responsible for two-quarters of false-negative cases and that mucinous carcinoma was the most common cause of false-negative scans. They stated that mucinous colorectal carcinoma has lower uptakes on FDG-PET imaging than non-mucinous carcinoma and that FDG-PET sensitivity for mucinous adenocarcinoma is much lower than non-mucinous carcinomas, which is completely consistent with the findings. PET/CT was also unable to identify vitality in sub centimetric hepatic focal lesions and pulmonary nodules, as well as the evaluation of mucinous tumor deposits, particularly in hypocellular lesions with extensive mucin, according to Lee et al. . The use of a delayed regional scan has recently been found to be more effective in detecting these metastases.
In investigation, patients who had combined treatment had a statistically significant higher false positive rate than those who received only chemotherapy (p-value = 0.033), but no statistically significant relation was established between the treatment of the investigated patients and the other findings.
The findings are consistent with those of Hetta et al. , who found that there were 60 patients in all, with 21 true positive cases, 37 true negative cases, one false-positive case, and one false-negative case. The false-positive case had positive long segment enhancing rectal mural thickening around the anastomotic site with high FDG uptake (high SUVmax), but it was later proven to be a negative case (colitis) after the second biopsy; the follow-up examination, done 6 months later with no treatment or further management, shows regressive course regarding the mural thickening and metabolic act. The false-negative case had low SUV-max at the collapsed rectosigmoid colon site and presacral soft tissue sheet; the known false-negative results of colorectal mucinous adenocarcinoma were concerning for a biopsy, which revealed positive tumor recurrence, and follow-up studies after chemotherapy showed uptake and size regression.
In investigation, the percentage of PET-CT metastases detected in the adenocarcinoma group was statistically significantly higher than in the mucinous group (65.4 percent, p-value = 0.014).
These findings matched those of Mittal et al. , who studied 73 patients (55 males, 18 females; age range 25 to 80 years) with histopathologically established CRC who received FDG PET/CT imaging for the identification of recurrence and/or metastasis after initial treatment. In 51 patients, rising CEA levels were found. PET/CT scans were positive in 13 patients (3 with liver lesions, 5 with lymph node involvement, 2 with bone metastases, 1 with local recurrence in the urinary bladder wall, 1 with lymph node and liver metastases, and 1 with lymph node and bone metastases), resulting in a change in management.
Going along with the findings of Chen et al. , who comprised 56 and 158 patients with a history of colorectal cancer who came with increasing CEA levels and conventional imaging modalities suggested an ambiguous reason for the elevated CEA level. PET/CT had a sensitivity of 98.1 percent and a specificity of 75 percent.
Chiewvit et al.  have shown that 18F-FDG PET/CT is a viable approach in postoperative evaluation of patients with suspected recurring colorectal malignant lesions and a normal CEA level, as previously reported and corroborated by the investigation. Local recurrences or metastases can be distinguished from postoperative alterations or benign disease features by 18F-FDG PET/CT.
As previously mentioned, PET/CT has been demonstrated to be useful in detecting post-therapeutic cancer colon recurrence and distant metastasis. PET/CT scans revealed greater information and better lesion characterization.