case_images: PMC9545900_01
case_images: Magnetic resonance imaging and histological findings before and after treatment. In the upper row, Magnetic resonance imaging-T2 scans at diagnosis and before surgery showed partial response of the tumor. In the lower row, representative sections of tumor specimens before neoadjuvant treatment (left) and after the treatment (right) (hematoxylin and eosin staining x 200). This patient had pathological complete response of the primary tumor.
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case_images: A 53-year-old man was diagnosed as having locally advanced rectal cancer in April 2021, which was 5.5 cm to the anal verge and staged as cT3N2 by magnetic resonance imaging (MRI) ( Figure 1 ). Four weeks after completion of the treatment, restaging MRI showed a partial response of the rectal lesion ( Figure 1 ). One week later, total mesorectal excision was performed, the pathological result showed a complete response ( Figure 1 ).
case_images: Immunohistochemical findings of primary tumor (A-H): Immunohistochemistry of the protein MLH1 (A), MSH2 (B), MSH6 (C), and PMS2 (D). MSH2 and MSH6 were positively expressed, whereas MLH1 and PMS2 were lacking (200x). (E) The combined positive score of programmed cell death protein ligand 1 (PD-L1) expression in rectal tumor before treatment was grade 2 (200x). Immunohistochemical analysis of the rectal tumor microenvironment before treatment (F) and the tumor microenvironment was enriched with CD8+ T cells in primary tumor (G) after completion of treatment (200x).
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case_images: MLH1 and PMS2, which meant that it was mismatch repair gene deficient (dMMR) ( Figures 2A-D ). Multiplex PCR-microsatellite analysis also confirmed the MSI-H status in all markers, and the combined positive score of programmed cell death protein ligand 1 expression was grade 2 ( Figure 2E ). T cells ( Figures 2F, G  ). The timeline of this case is shown in  Figure 4 .
case_images: Clinical diagnosis and histological results of liver metastases (A-E). (A, B) Dynamic-enhanced magnetic resonance imaging shows liver metastasis after neoadjuvant treatment and confirmed by contrast-enhanced ultrasonography. (C) Contrast-enhanced computed tomography shows no definite liver metastases before neoadjuvant treatment. (D) The tumor microenvironment was enriched with CD8+ T cells in liver metastases after completion of treatment (200x). (E) Post-treatment liver biopsy shows hepatic lobular structure with normal architecture, and no tumor cells were observed (200x).
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case_images: The lesion size was 1.5 cm x 1.3 cm in MRI ( Figures 3A, B  ). A reexamination of the baseline computed tomography of abdomen was performed and a nearly invisible, obscure lesion was detected at the corresponding location, which could represent the early stage of metastases (classified as suspicious metastases:Mx) ( Figure 3C ). Examination of fine-needle aspiration biopsy showed hepatic lobular structure with many lymphocyte infiltration, especially CD8-positive T cells ( Figure 3D ). No tumor cells were observed ( Figure 3E ).
case_images: Timeline of disease status and corresponding treatment regimens. XELOX, capecitabine and oxaliplatin; TME, total mesorectal excision; pCR, pathological complete response.
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case_images: T cells ( Figures 2F, G  ). The timeline of this case is shown in  Figure 4 .