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Objective:
Some cancer cells, including colorectal cancer (CRC) cells are said to contain mobile lipids, which is claimed to be an early indicator of the effects of chemotherapy. Because of the various effects of modern chemotherapy, universal biomarkers, and more effective predictors of response to chemotherapy are required in patients with colorectal liver metastases (CRLM). The aim of the study was to investigate the incidence and clinical significance of intratumoral fat deposition in CRLM after chemotherapy using dual-echo gradient-recalled echo MRI.

Materials and Methods:
The study was a single-center retrospective analysis of 43 consecutive patients with CRLM diagnosed between 2020 and 2021 (28 men, mean age: 64.2 ± 10.8 years) undergoing MRI after preoperative chemotherapy. On dual-echo gradient-recalled echo MR images, intratumoral fat deposition and fat signal fraction at the densest areas of fat deposition in colorectal liver metastases were evaluated. Signal intensity drop of 12% or greater in opposed-phase images compared to in-phase images was considered as indicative of the presence of intratumoral fat. Predictors of intratumoral fat deposition were identified by multivariate analyses. The presence of fat deposition was correlated with overall survival of patients.

Results:
Before and after chemotherapy, 0 (0%) and 15 (34.88%) of the patients exhibited intratumoral fat deposition, respectively, including 11 men and 5 women, respectively. The number of metastases ranged from 1 - 20 with a mean number of 4. The size of metastases ranged from 11 - 116 mm with a mean size of 29.74 ± 24.36 mm. Patients primarily underwent chemotherapy following the FOLFOX-4 (folinic acid - leucovorin, 5-fluorouracil and oxaliplatin) (<em>N</em> = 25) and FOLFIRI (folinic acid - leucovorin, 5-fluorouracil and irinotecan) (<em>N</em> = 14) protocol. The independent predictor of intratumoral fat deposition was the lesion size (<em>p</em> = 0.010): 30 mm in the fat group and 24 mm in the nonfat group. An additional factor related to intratumoral fat deposition was the number of liver metastases of 4 or more (<em>p</em> = 0.005). Although the mortality was higher in fat group: 10 (66.67%) vs. 10 (35.71%), <em>p</em> < 0.001, survival was prolonged in nonfat group: 18 (64.29%) vs. 5 (33.33%), <em>p</em> < 0.001.

Conclusion:
In our group 34.88% of patients with CRLM after systemic therapy exhibited intratumoral fat deposition. This phenomenon was frequently identified in CRLM on MR images acquired after preoperative chemotherapy which corresponds with impaired outcome. Further studies, comprising larger patients’ groups, are required to determine if the development of intratumoral fat deposition in CRLM after chemotherapy correlates with long-term prognosis.