Mycosis Fungoides: CS-Ext and CS-SSF1

Mycosis fungoides (9700/3), also known as Alibert-Bazin syndrome, is the most common type of primary cutaneous T-cell lymphoma.  The name Mycosis fungoides loosely means “mushroom-like fungal disease.”

It is so named because the skin tumors, particularly of severe cases, have mushroom-like appearance.   However, it is not a fungal infection but rather a type of non-Hodgkins lymphoma.

M.D., CTR, VP of Cancer Registry Elizabeth Patena, M.D., CTR, VP of Cancer Registry

It occurs when certain immune cells, called T cells, become cancerous; these cancers characteristically affect the skin, causing different types of skin lesions. Although the skin is involved, the skin cells themselves are not cancerous. The cause of mycosis fungoides is unknown, but it is not believed to be hereditary or genetic in the vast majority of cases.

Mycosis fungoides progresses slowly through several stages, although not all people with the condition experience all stages.  Most affected individuals initially develop skin lesions called patches, which are flat, scaly, pink or red areas on the skin that can be itchy.  Cancerous T cells, which cause the formation of patches, are found in these lesions.

The skin problems result when cancerous T cells move from the blood into the skin.  In most affected individuals, patches progress to plaques, the next stage of mycosis fungoides.  Plaques are raised lesions that are usually reddish, purplish, or brownish in color and itchy. Plaques commonly occur in the same body regions as patches.  While some plaques arise from patches, others develop on their own, and an affected person can have both patches and plaques simultaneously.

As with patches, cancerous T cells are found in plaques.  Plaques can remain stable or can develop into tumors. Not everyone with patches or plaques develops tumors.

The tumors in mycosis fungoides, which are composed of cancerous T cells, are raised nodules that are thicker and deeper than plaques. They can arise from patches or plaques or occur on their own.


CS-Ext and CS-SSF1

In Collaborative Staging, CS Ext describes the involvement of the skin – from patches to plaques to tumors.   CS-SSF 1 describes peripheral blood involvement (blood tumor burden) and T cell clonality.  Information about peripheral blood involvement and T-cell clonality identified by polymerase chain reaction (PCR) or Southern blot analysis is combined in a “B” category unique to mycosis fungoides staging in the TNM system.

Assessing the Tumor

Assessment of blood tumor burden is performed using two types of tests:

– Microscopically to count neoplastic (Sezary) cells. The results can be given as counts per cubic millimeter (mm3) or as a percentage of the total lymphocytes that are abnormal Sezary cells.

– Flow cytometry to characterize the cell surface markers on the neoplastic cells, where the neoplastic cells show the loss of some specific markers (for example, CD26).

The basic categories are B0 (no significant blood involvement); B1 (low blood tumor burden); and B2 (high blood tumor burden).  Any mention of B2 puts the case into Stage IV.  B0 and B1 are subcategorized by clonality.

In the sixth edition of AJCC and CS version 1, mycosis fungoides site-specific factor 1 described only the presence or absence of Sezary cells in circulating blood. In the seventh edition of AJCC and CS version 2, the structure of SSF1 is more complex.

Codes 001 to 003 have been made obsolete and new codes and definitions have been created to account for peripheral blood involvement and clonality. The lack of monoclonality (clone negative) generally indicates a better prognosis.

Coding Guidelines

Code a statement of peripheral blood involvement and clonality (if given) as reported by the clinician from tissue and/or blood samples. If the physician does not provide a B rating but counts or percentages of neoplastic cells, flow cytometry test results, and/or clonality test results are performed, use the appropriate code for the amount of blood involvement with “clone unknown”.

Codes 010 – 030: Absence of significant blood involvement (no peripheral blood involvement)
010 Clone negative; Stated as B0a

  • includes ≤ 5% atypical (Sezary) cells in peripheral blood, clone negative
020 Clone positive; Stated as B0b

  • includes ≤ 5% atypical (Sezary) cells in peripheral blood, clone positive
030 Clone unknown; Stated as B0 [NOS]

  • < 1000 Sezary cells
  • includes ≤ 5% atypical (Sezary) cells in peripheral blood, clone unknown
Codes 040 – 060: Low blood tumor burden: more than 5% of peripheral blood lymphocytes are atypical (Sezary) cells but does not meet the criteria of B2
040 Clone negative; Stated as B1a
050 Clone positive; Stated as B1b
060 Clone unknown; Stated as B1 [NOS]
Additional codes
070 High blood tumor burden: 1000/uL Sezary cells or more with positive clone; Stated as B2
080 Percent of atypical peripheral blood lymphocytes not stated and B rating not stated
090 Sezary cell counts, blood flow cytometry, and/or clonality results in chart, B rating not stated
997 Sezary cell counts, blood flow cytometry, and/or clonality tests ordered, test results not in chart, B rating not known
999 Unknown or no information; not documented in patient record


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