Skin: AJCC8 melanoma T staging

Free question published 21 September 2026

SkinAJCC8 melanoma T staging

A 49-year-old woman has an excision biopsy of a changing mole on her shoulder. Histopathology reports a cutaneous melanoma with a Breslow thickness of 0.6 mm, no ulceration, and a mitotic rate of 4 per mm2. There is no clinical evidence of nodal or distant disease. Which T category should be assigned to this primary tumour?

AT1a
BTis (in situ)
CT1b
DT2a
ET2b

Why A is correct

Under AJCC 8th edition, T1a is a non-ulcerated melanoma less than 0.8 mm thick. Crucially, mitotic rate is no longer used to subcategorise T1 melanomas, so a high mitotic rate does not upstage a 0.6 mm non-ulcerated tumour to T1b. This lesion is therefore T1a.

And why the others are not

BIncorrect: an invasive melanoma with a measurable Breslow thickness is not in situ (Tis).
CIncorrect: T1b is 0.8-1.0 mm (any ulceration status) or under 0.8 mm with ulceration; this lesion is under 0.8 mm and non-ulcerated, and mitotic rate does not apply.
DIncorrect: T2 applies to tumours greater than 1.0 mm up to 2.0 mm, which this 0.6 mm lesion is not.
EIncorrect: T2b requires a 1.0-2.0 mm ulcerated tumour, neither of which applies here.

Source AJCC 8th edition melanoma staging - key changes — Gershenwald JE, Scolyer RA, Hess KR, et al. Melanoma staging: Evidence-based changes in the American Joint Committee on Cancer eighth edition cancer staging manual. CA Cancer J Clin. 2017;67(6):472-492.