Table of Contents
Mycosis fungoides – Spot/plaque stage
LEGEND
Papillary dermal fibrosis is present.
In the patch or plaque stage, there is a perivascular and lichenoid infiltrate of atypical lymphocytes in the superficial and mid-dermis, with prominent epidermotropism.
The epidermis does not show a reactive response to this infiltrate — spongiosis is absent.
Mycosis fungoides – Patch-plaque stage
LEGEND
In the plaque stage, there may be acanthosis and elongation of rete ridges.
Pautrier microabscesses (collections of atypical lymphocytes within the epidermis) are observed.
Lymphocytes often appear haloed and display a linear arrangement along the basal membrane.
Mycosis fungoides – Patch-plaque stage – high magnification
LEGEND
Lymphocytes are highly atypical, with large, hyperchromatic nuclei.
Mycosis fungoides – Patch-plaque stage
CD3 is positive, highlighting the epidermotropism (the tendency of lymphocytes to invade the epidermis).
Mycosis fungoides – Tumor stage
LEGEND
In the tumor stage, the lymphocytic infiltrate extends through the entire dermis and may involve the subcutaneous tissue.
Epidermotropism and Pautrier microabscesses may still be observed but are less frequent than in the patch-plaque stage.
Mycosis fungoides – Tumor stage
LEGEND
Lymphocytes are atypical, very large (almost as large as keratinocytes), hyperchromatic, and irregular.
Mycosis fungoides
T-cell markers such as CD2, CD3, CD5, and CD7 are generally positive.
Here’s an example of a positive CD3
Mycosis fungoides
There is often an increased proportion of CD4+ T-cells, with a CD4:CD8 ratio > 3:1.
CD4 expression is positive, as shown in the example.
Mycosis fungoides
There can be loss of expression of certain T-cell markers, particularly CD7 or CD5.
This sample demonstrates reduced CD7 expression compared to CD3.
