Melanoma Staging — SCE Dermatology MCQ

Correct answer: A — T1b

The correct answer is A, T1b. Under AJCC 8th edition, T1 melanomas are subdivided at the 0.8 mm Breslow thickness threshold: T1a is non-ulcerated and under 0.8 mm, whereas T1b covers tumours 0.8 to 1.0 mm in thickness regardless of ulceration status, or tumours under 0.8 mm if ulcerated. This tumour measures 0.9 mm, which falls within the 0.8 to 1.0 mm band, so it is classified T1b on thickness alone, and the presence of ulceration reinforces this (it would also be T1b even without ulceration). This distinction matters clinically because T1b thickness or ulceration status determines whether sentinel lymph node biopsy should be discussed with the patient, per current UK and international melanoma management pathways. Why the other options are wrong: C. T2b: T2 category requires Breslow thickness greater than 1.0 mm up to 2.0 mm; 0.9 mm does not reach this threshold regardless of ulceration. D. T2a: Same thickness error as T2b; T2a requires thickness over 1.0 mm up to 2.0 mm without ulceration, which does not apply to a 0.9 mm tumour. E. T1a: T1a is reserved for non-ulcerated melanomas under 0.8 mm; this tumour is both thicker than 0.8 mm and ulcerated, excluding T1a on two counts. B. T3a: T3 category requires thickness over 2.0 mm up to 4.0 mm, far exceeding the 0.9 mm measured here. Key point: any melanoma measuring 0.8 to 1.0 mm in Breslow thickness is staged T1b regardless of ulceration, while under 0.8 mm requires ulceration to be upstaged from T1a to T1b.

Reference: College of American Pathologists, Protocol for the Examination of Specimens From Patients With Melanoma (based on AJCC 8th edition), 2017: T1b melanomas are defined as 0.8-1.0mm in thickness or ulcerated melanomas under 0.8mm. https://documents.cap.org/protocols/cp-melanoma-skin-2017-v4000.pdf