Cutaneous T cell lymphomas (CTCLs) are a group of heterogeneous, life-threatening, extra-nodal and lymphoproliferative T cell neoplasms. Since chronic inflammation serves a key role in CTCL progression, curcumin, a natural pigment with proven anti-inflammatory and antineoplastic properties, as well as minimal toxicity, may be used as a therapeutic agent. In the present study, two formulations of curcumin (standard ethanolic and a Pluronic ®P-123/F-127 micellar solution) were compared regarding their cytotoxic efficacy and speed of internalization in three CTCL cell lines, namely HuT-78, HH and MJ. In addition, the modulating effect of curcumin on selected proteins involved in the proliferation and progression of the disease was determined. The results indicated the superiority of the Pluronic ®P-123/F-127 micellar curcumin over the standard ethanol solution in terms of cellular internalization efficiency as determined by spectrophotometric analysis. Notably, the presence of commonly used media components, such as phenol red, may interfere when interpreting the cytotoxicity of curcumin, due to their overlapping absorbance peaks. Therefore, it was concluded that phenol red-free media are superior over media with phenol red in order to correctly measure the cytotoxic efficacy and cell penetration of curcumin. Depending on the cell line, the IC 50 values of micellar curcumin varied from 29.76 to 1.24 µΜ, with HH cells demonstrating the highest sensitivity. This cell line had the lowest expression levels of the Wilms' tumor-1 transcription factor. Performing western blot analyses of treated and untreated CTCL cells, selective signal transduction changes were recorded for the first time, thus making curcumin nano-formulation an attractive and prospective option with therapeutic relevance for CTCL as a rare orphan disease.