8th Edition MCC Staging System Announced

Overview

As of January 2018, the AJCC 8th edition staging system will replace the 7th edition staging system. MCC patients will be categorized by their extent of disease at diagnosis (stage) as summarized in the 8th Edition table (see below) starting in 2017. The 2017 MCC staging system was based on an analysis of over 9,000 patients using the National Cancer Database as well as extensive review of the literature.¹

There are two very important differences of the updated 8th edition staging system:

1) For the new system, it is important to designate if the stage was determined ‘clinically’ or ‘pathologically’. This has important implications in recurrence and survival. For example, if lymph nodes are only ‘clinically negative’ (doctors can not feel abnormal nodes on physical exam) this is less accurate than ‘pathologically negative’ nodes because microscopic MCC spread to nodes is present in one third of “clinically negative” nodes. Because ‘pathologically’ node negativity is thus more accurate, patients whose nodes are negative pathologically have a lower chance of experiencing a recurrence as compared to ‘clinically’ node negative patients because one third of these actually have early disease in their nodes.

2) Patients with nodal disease but no known primary tumor (‘unknown primary’) are now staged separately from patients that have nodal and a ‘known’ primary tumor. There are many studies that have shown that node-positive patients with an unknown primary tumor have an improved survival outcome compared to node-positive patients who have a visible tumor.²³⁴ For this reason, these two subtypes of stage III disease are separated.

Determining the 8th edition stage of Merkel cell carcinoma

MCC is divided into stages based on the primary tumor size and extent of disease (present in lymph nodes and or present at distant sites in the body). Furthermore, the 8th edition staging system is divided into how the disease was detected, either clinically or pathologically. Clinical stages can be determined by inspection, palpation of (feeling) the lymph nodes, or imaging studies. In contrast, pathological stages are based on microscopic study of tissue obtained by lymph node biopsy, or by needle biopsy.

The stage at diagnosis is the major determinant of the chance for later spread (metastasis) and treatment options.

8th Edition MCC Staging Sytem Table

* Clinical detection of nodal or metastatic disease may be via inspection, palpation, and/or imaging
**Pathological detection/confirmation of nodal disease may be via sentinel lymph node biopsy, lymphadenectomy, or fine needle biopsy; and pathological confirmation of metastatic disease may be via biopsy of the suspected metastasis
***In transit metastasis: a tumor distinct from the primary lesion and located either (1) between the primary lesion and the draining regional lymph nodes or (2) distal to the primary lesion

Click here to download the 8th edition staging system.

Understand the science

There are many studies that have shown that node-positive patients with an unknown primary tumor have an improved survival outcome compared to node-positive patients who have a visible tumor (Chen et al. 2013, Foote et al. 2011, and Tarantola et al. 2012). Several lines of evidence suggest that the reason for this is that the immune system eliminated the primary tumor in the ‘unknown primary’ cases, and the immune system is thus better able to eliminate other microscopic disease that may have spread elsewhere in the body.

What to do next

If a patient has just had an initial biopsy diagnosed as MCC, it is likely they can only be staged ‘clinically’. In most cases, a sentinel lymph node biopsy should be considered.