Dr Raymond Yap( left) Colorectal and general surgeon based in Melbourne, Victoria.

Dr Ben Markman( right) Medical oncologist, The Alfred Hospital and Cabrini Hospital, Melbourne, Victoria.

Copyright © 2025 Australian Doctor All rights reserved. No part of this publication may be reproduced, distributed, or transmitted in any form or by any means without the prior written permission of the publisher. For permission requests, email: howtotreat @ adg. com. au.

This information was correct at the time of publication: 11 April 2025

BACKGROUND

TREATMENT of colorectal cancer has

become increasingly personalised over the past 20 years. Although initial workup and staging has largely stayed the same with the need for tissue biopsy( usually via colonoscopy) and staging with CT scanning, treatment has become a more complicated affair, with questions over timing of surgery versus chemotherapy, the role of radiotherapy and the emerging use of immunotherapy. Nonetheless, these developments have improved colorectal cancer survival, particularly in stage III and stage IV cancers.

This How to Treat is part two of a two-part series. Part one covered the diagnosis and investigation of colorectal cancer, as well as covering common indications for screening and colonoscopy. This article covers the treatment and management of colorectal cancer. It aims to equip GPs to aid patients in their treatment journey, as well as identify common complications.

PREOPERATIVE STAGING

COLORECTAL cancer is staged using

the TNM staging system( see table 1),

Table 1. TNM classification for colorectal cancer

T Primary tumour

N Regional lymph nodes

M Distant metastases

Source: American Cancer Society 1

which generally guides the prognosis

and the need for adjuvant chemotherapy

. There are subtle differences between colonic and rectal cancers that also require consideration.

Colon cancers, if considered curable( no metastatic disease or irresectable local disease), generally proceed to surgical resection, with decisions on chemotherapy

TX: Primary tumour cannot be assessed TO: No evidence of primary tumour Tis: Carcinoma in situ T1: Tumour invades submucosa T2: Tumour invades muscularis propria T3: Tumour invades through muscularis propria into the subserosa or non-peritonealised pericolic or perirectal tissues

T4: Tumour directly invades other organs or structures and / or perforates visceral peritoneum

NX: Regional nodes cannot be assessed N0: No regional node metastasis N1: Metastasis in 1-3 regional lymph nodes N2: Metastasis in four or more regional lymph nodes

MX: Distant metastasis cannot be assessed M0: No distant metastasis M1: Distant metastasis

determined by staging. Rectal cancers in the intraperitoneal rectum( upper third), generally behave like colonic cancers and are treated similarly. Conversely, extraperitoneal rectal cancers( lower two-thirds), have a higher risk of local recurrence, and consideration is therefore given to neoadjuvant treatment with chemoradiation.

WORKUP

Preoperative workup of colonic cancer

ONCE a histological diagnosis of cancer

is made, staging is performed with a carcinoembryonic antigen( CEA) and a CT chest, abdomen and pelvis to rule out metastatic disease( see figure 1). FBC, EUC, LFTs and ECG are usually performed to assess the surgical risk.

Sometimes a biopsy is equivocal. If the lesion appears clinically malignant, resection may proceed on that basis. Alternatively, a repeat colonoscopy may be performed to remove more tissue; however, if the lesion cannot be removed colonoscopically, a resection may still be required. PET scanning is not routinely required in these patients but may be helpful in patients where findings are equivocal on preoperative CT scanning. Equivocal liver lesions may also be evaluated with MRI.

Preoperative workup for rectal cancer

Extraperitoneal rectal cancers

require further evaluation because their risk of local recurrence is higher. A dedicated rectal MRI