Staging colorectal cancer with the TNM 7(th): the presumption of innocence when applying the M category

Abstract

One of the main changes of the current TNM-7 is the elimination of the category MX, since it has been a source of ambiguity and misinterpretation, especially by pathologists. Therefore the ultimate staging would be better performed by the patient's clinician who can classify the disease M0 (no distant metastasis) or M1 (presence of distant metastasis), having access to the completeness of data resulting from clinical examination, imaging workup and pathology report. However this important change doesn't take into account the diagnostic value and the challenge of small indeterminate visceral lesions encountered, in particular, during radiological staging of patients with colorectal cancer. In this article the diagnosis of these lesions with multiple imaging modalities, their frequency, significance and relevance to staging and disease management are described in a multidisciplinary way. In particular the interplay between clinical, radiological and pathological staging, which are usually conducted independently, is discussed. The integrated approach shows that there are both advantages and disadvantages to abandoning the MX category. To avoid ambiguity arising both by applying and interpreting MX category for stage assigning, its abandoning seems reasonable. The recognition of the importance of small lesion characterization raises the need for applying a separate category; therefore a proposal for their categorization is put forward. By using the proposed categorization the lack of consideration for indeterminate visceral lesions with the current staging system will be overcome, also optimizing tailored follow-up.

Keywords: Colorectal cancer; Imaging; Indeterminate lesions; Metastases; Staging.

Figure 1

Example of a small lesion which proved to be benign after follow-up. A: Two small (< 10 mm) indeterminate focal liver lesions (white arrow) on contrast-enhanced computed tomography; B: Corresponding magnetic resonance imaging (MRI), images showing a T2w Turbo Spin Echo sequence with fat suppression. Two clearly hyperintense focal liver lesions (white arrow) are displayed compatible with simple liver cysts; C: Corresponding MRI images showing a T2w Turbo Spin Echo sequence without fat suppression. Two clearly hyperintense focal liver lesions (white arrow) are displayed compatible with simple liver cysts.

Figure 2

Example of a small lesion which proved to be malignant after follow-up. A: Positron emission tomography (PET)/computed tomography negative (PET-cold) focal liver lesion (white arrow) in a patient who received chemotherapy in the past; B: Corresponding T1w Gradient Echo magnetic resonance imaging (MRI) image before injection of contrast agent shows a rather hypo-intense focal liver lesion (white arrow); C: Corresponding T1w Gradient Echo MRI image in the venous phase after injection of contrast agent shows a hypo-intense focal liver lesion with ring-enhancement compatible with an (active) malignant focal liver lesion (colorectal cancer liver metastasis) (white arrow).

Figure 3

Restaging the liver after neoadjuvant therapy in a patient with multiple liver metastases from rectal cancer. A: On computed tomography (CT) before intravenous contrast, all the metastases disappeared except for a small lesion suspicious of residual disease (white arrow); B: Corresponding CT after intravenous contrast showing the challenging lesion (white arrow); C: Also on magnetic resonance imaging the lesion (white arrow) remains suspicious for malignancy providing indication for a liver resection.

Figure 4

Pathological examination of the resected liver specimen corresponding to the lesion indicated by the white arrow in figure 3. A: Gross specimen: on cut the macroscopic examination shows a star-like whitish lesion; B: At histology (hematoxylin and eosin, x 100) only fibrosis and inflammation are seen indicating a complete response to chemotherapy.