Currently, these lesions are all now more uniformly referred to as IT disease. IT disease can be heterogeneous in both the size and number of lesions, with most lesions ranging from 0.2 cm to 3 cm and the possibility that an individual patient may have one to more than 100 lesions. IT disease includes local recurrences within 2 cm of the primary lesion as well as multiple small lesions between the primary and regional nodal basin, which are frequently referred to as satellitosis.

After appropriate initial surgical therapy for primary melanoma, approximately 4% to 10% of patients develop IT disease at a median time of 18 months after primary excision.1 IT metastases are considered to be American Joint Committee on Cancer (version 8) stage N1c (IIIB) without regional nodal involvement, stage N2c (IIIC) with one regional lymph node (LN) involved, and stage N3c (IIIC) with two or more regional LNs involved.

Treatment of IT disease depends on several factors: concurrent distant disease, concurrent nodal disease, location of IT disease (extremity or not), volume of IT disease and disease burden, timing of recurrence relative to primary or prior IT melanoma excisions, and overall patient performance status. Evaluation of a patient who presents with IT disease should begin with an assessment of disease burden by physical examination and whole-body imaging.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5952330/