Introduction

Stage versus Category versus Classification

• Stage for a cancer is determined from the aggregate of its extent with respect to the tumor (T), lymph nodes (N), and metastases (M).
• Category describes each of the T, N, and M designations.
  • Stage is often used erroneously to describe the individual T/N/M category designations (eg. 'T staging', 'N staging'), which is incorrect. Only the aggregate information resulting from the T, N, and M category designations should be assigned an overall stage.
  • The term subcategory is used to describe further divisions within the individual T/N/M categories. For instance, in melanoma: N1a, N1b, N1c.
• Classification describes the specific time point at which the staging information was collected.
• There are 5 specific classifications within the AJCC 8^th Edition Staging System:
  1. Clinical (cTNM): based on history, examination, and imaging done prior to initiation of treatment
  2. Pathological (pTNM): based on clinical stage information supplemented/modified by operative and pathological evaluation of the resected specimens.
  3. Post-therapy or Post-Neoadjuvant Therapy (ycTNM and ypTNM): In patients that are receiving systemic or radiation therapy alone, or who are being staged post neoadjuvant therapy but prior to planned surgery, a 'y' prefix is used. ycTNM refers to clinical staging post-therapy/post-neoadjuvant therapy, while ypTNM refers to pathological staging in patients who get surgery following neo-adjuvant therapy.
  4. Recurrence or Retreatment (rTNM): Patients that have a recurrence or disease progression that are re-staged are given an 'r' prefix.
  5. Autopsy (aTNM): Staging classifcation for cancers identified only at autopsy.
• Of these, the clinical and pathological classifications are by far the most used.

• In the T-categorization of tumours, whenever a size range is provided (eg. 2-4 cm), it will almost always be exclusive for the lower value, and inclusive for the upper value, with very few exceptions.
  • For instance, T2 p16- oropharynx cancer is > 2 cm but ≤ 4 cm in greatest dimension.
  • One exception for this rule would be T1b cutaneous melanoma, which has a thickness threshold of 0.8 mm - 1.0 mm which is inclusive of both the lower and higher value.
• Many disease sites use the same nodal and group categorization system, which is described in the next chapter.