PMC10359816_01
Rectal signet ring cell carcinoma. Computed tomography images at the initial diagnosis (A) and after the implementation of neoadjuvant therapy (B). Hematoxylin & eosin staining imparting a signet ring appearance (C, magnification power: 20x; D, magnification power: 40x). Immunohistochemical staining revealing (E) CK20 (+), and (F) CDX-2 (+) (magnification power: 20x).
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Computed tomography (CT) of the chest and abdomen and magnetic resonance imaging (MRI) of the pelvic confirmed the tumor stage of cT3N1M0 ( Figure 1A ). Laparoscopic abdominoperineal resection (R0) with a permanent colostomy was performed for her 6 weeks after the termination of neoadjuvant therapy ( Figure 1B ). Tumor Regression Grade 2) was determined via postoperative pathologic findings ( Figures 1C-F ). Two out of eighteen mesorectal lymph nodes were identified with tumor involvement.
Right breast and vulvar metastases from rectal signet ring cell carcinoma. (A) Computed tomography image showing the right breast metastasis. Hematoxylin & eosin staining demonstrating morphological characteristics of (B) the right breast and (F) vulvar metastases similar with the primary rectal carcinoma (magnification power: 20x). Immunohistochemical staining: (C) CK20 (+) (magnification power: 20x), (D) CDX-2 (+) (magnification power: 20x), and (E) GATA3 (-) (magnification power: 100x) of the right breast metastasis tissue; (G) CK20 (+) (magnification power: 40x), (H) CDX-2 (+) (magnification power: 20x), and (I) Alcian Blue (+) (magnification power: 20x) of the vulvar metastasis tissue.
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The follow-up CT examination found the right breast mass ( Figure 2A ). Hematoxylin & eosin and immunohistochemical (IHC) staining indicated the metastases to the breast (positive: CK20, CDX-2, E-cadherin; negative: CK7, PR, ER, Her-2, GATA3, GCDFP15) ( Figures 2B-E ) and vulva (positive: CDX-2, PCK, CEA, Alcian Blue) ( Figures 2F-I ) from rectal SRCC.
Timeline with clinical data from the episode of care. SRCC, signet ring cell carcinoma; TRG2, tumor regression grade 2; pMMR, proficient mismatch repair; IHC, immunohistochemical; MSI-L, microsatellite instability-low; CT, computed tomography.
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Though limited sensitivity, the reduction of tumor markers at the early phase represented favorable response to neoadjuvant therapy, while the elevation of tumor markers at the late phase indicated rapidly progressive disease. The timeline with clinical data from the episode of care is shown in  Figure 3 .