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Stage Information for Merkel Cell Carcinoma

Previously, five competing staging systems have been used to describe Merkel cell carcinoma (MCC) in most publications.

Table 2. Five Previously Used Competing Merkel Cell Carcinoma Staging Systems

First AuthorPublication DateInstitution(s)No. of Patients in Case SeriesDates of Cases
MSKCC = Memorial Sloan Kettering Cancer Center; N/A = Not applicable.
a The MSKCC system has evolved over time. MSKCC authors have published one additional case series with 256 patients.[1]
Yiengpruksawan et al.[2]1991MSKCCa771969–1989
Allen et al.[3]1999MSKCCa1021969–1996
Allen et al.[4]2005MSKCCa2501970–2002
American Joint Committee on Cancer[5]2002N/AN/A 
Clark et al.[6]2007Westmead Hospital, Sydney, Australia110 
Princess Margaret Hospital/University Health Network, Toronto, Canada
Sydney Head and Neck Cancer Institute/Royal Prince Alfred Hospital, Sydney, Australia

These staging systems are highly inconsistent with each other. Indeed, stage III disease can mean anything from advanced local disease to nodal disease to distant metastatic disease. Furthermore, all MCC staging systems in use have been based on fewer than 300 patients.

Definitions of TNM

To address these concerns, a new MCC-specific consensus staging system was developed by the American Joint Committee on Cancer (AJCC) to define Merkel cell carcinoma, as shown in tables 3, 4, 5, and 6.[7] Prior to the publication of this new system, the AJCC advocated using the nonmelanoma staging system.

Table 3. Primary Tumor (T)a

a Reprinted with permission from AJCC: Merkel cell carcinoma. In: Edge SB, Byrd DR, Compton CC, et al., eds.: AJCC Cancer Staging Manual. 7th ed. New York, NY: Springer, 2010, pp 315-23.
TXPrimary tumor cannot be assessed.
T0No evidence of primary tumor (e.g., nodal/metastatic presentation without associated primary).
TisIn situ primary tumor.
T1≤2 cm maximum tumor dimension.
T2>2 cm but ≤5 cm maximum tumor dimension.
T3>5 cm maximum tumor dimension.
T4Primary tumor invades bone, muscle, fascia, or cartilage.

Table 4. Regional Lymph Nodes (N)a

a Reprinted with permission from AJCC: Merkel cell carcinoma. In: Edge SB, Byrd DR, Compton CC, et al., eds.: AJCC Cancer Staging Manual. 7th ed. New York, NY: Springer, 2010, pp 315-23.
b Clinical detection of nodal disease may be via inspection, palpation, and/or imaging.
c Micrometastases are diagnosed after sentinel or elective lymphadenectomy.
d Macrometastases are defined as clinically detectable nodal metastases confirmed by therapeutic lymphadenectomy or needle biopsy.
e 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.
NXRegional lymph nodes cannot be assessed.
N0No regional lymph nodes metastasis.
cN0Nodes negative by clinical examb(no pathologic node exam performed).
pN0Nodes negative by pathologic exam.
N1Metastases in regional lymph node(s).
N1aMicrometastasis.c
N1bMacrometastasis.d
N2In transit metastasis.e
1|2

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