What is the TNM (Tumor‑Node‑Metastasis) classification for a rectal adenocarcinoma with circumferential wall thickening that has breached the muscularis propria, 2.5 cm extramural extension into perirectal fat, presacral and pararectal lymph node involvement, calcification, and no distant metastases?

TNM Classification for Rectal Adenocarcinoma with Presacral and Pararectal Lymph Node Involvement

Based on the clinical description of circumferential wall thickening breaching the muscularis propria with 2.5 cm extramural extension, presacral and pararectal lymph node involvement, and no distant metastases, this tumor is classified as T3d N1 M0 (Stage IIIB).

T-Stage Classification

The tumor is classified as T3d because it demonstrates invasion through the muscularis propria into the perirectal fat with 2.5 cm (25 mm) of extramural extension. 1, 2

• T3 is defined as tumor invasion through the muscularis propria into the subserosa or non-peritonealised perirectal tissues. 1, 2
• The ESMO guidelines recommend subclassification of T3 tumors based on depth of extramural invasion: T3a (<1 mm), T3b (1-5 mm), T3c (6-15 mm), and T3d (>15 mm). 1
• With 2.5 cm (25 mm) of extramural extension, this clearly exceeds the 15 mm threshold for T3d classification. 1
• The presence of calcification does not alter the T-stage classification but may represent tumor necrosis or dystrophic changes. 3

N-Stage Classification

The presacral and pararectal lymph nodes indicate regional lymph node metastasis, classified as at least N1. 1

• N1 is defined as metastasis in 1-3 regional lymph nodes. 1
• N1a indicates metastasis in 1 regional lymph node, while N1b indicates metastasis in 2-3 regional lymph nodes. 1
• Without knowing the exact number of involved lymph nodes from your description, the classification is N1 (either N1a or N1b depending on whether 1,2, or 3 nodes are involved). 1
• If 4 or more regional lymph nodes are involved, the classification would be N2 (N2a for 4-6 nodes, N2b for 7 or more nodes). 1
• Presacral and pararectal lymph nodes are considered regional lymph nodes for rectal cancer. 1, 4

M-Stage Classification

The absence of distant metastases classifies this as M0. 1

• M0 indicates no distant metastasis. 1
• M1 would indicate distant metastasis, with M1a for single organ involvement, M1b for multiple organs, and M1c for peritoneal metastases. 1

Overall Stage Grouping

This tumor is Stage IIIB (T3d N1 M0). 1, 4

• Stage III disease indicates any T stage with N1-2 and M0. 4
• The specific substage depends on the T and N categories, with T3d N1 M0 falling into Stage IIIB. 1

Clinical Implications and Treatment Approach

This locally advanced rectal cancer requires neoadjuvant chemoradiotherapy followed by total mesorectal excision (TME). 1, 5

• Preoperative chemoradiotherapy is strongly preferred over postoperative treatment because it is more effective and less toxic. 1, 5
• Two acceptable neoadjuvant approaches exist: short-course radiotherapy (25 Gy in 5 fractions over 1 week) followed by immediate surgery, or long-course chemoradiotherapy (45-50.4 Gy with concurrent 5-FU) followed by surgery 6-8 weeks later. 1, 5
• TME with sharp dissection along the mesorectal fascia is mandatory, with achievement of negative circumferential resection margins (>1 mm clearance). 1, 5
• At least 12 lymph nodes should be examined pathologically. 1, 4
• Adjuvant chemotherapy should be administered postoperatively for this Stage III disease. 5, 4

Critical Staging Considerations

Pelvic MRI is the most accurate modality for preoperative staging and should assess the circumferential resection margin (CRM) status. 1

• MRI can accurately differentiate T3 from T4 disease and assess the relationship between tumor and mesorectal fascia. 1, 3
• A clear CRM is defined as >1 mm from the mesorectal fascia, while an involved CRM is within 1 mm. 1
• Anterior rectal tumors with thin perirectal fat may be more difficult to stage accurately on MRI and should be interpreted with caution. 6
• Extramural vascular invasion (EMVI) detection on MRI predicts higher risk of distant metastases and should be documented. 1