Non-melanocytic skin tumours
How ultraviolet light mutates keratinocytes, how benign seborrhoeic keratosis differs from the dysplasia of actinic keratosis and Bowen disease, and why squamous cell carcinoma can spread to nodes while basal cell carcinoma destroys locally.
By the end, you can
- Explain how ultraviolet light causes the characteristic mutations of skin cancer and why TP53-mutant clones expand.
- Distinguish seborrhoeic keratosis, actinic keratosis and Bowen disease by their microscopic appearance and behaviour.
- Describe the gross and microscopic appearance of cutaneous squamous cell carcinoma and basal cell carcinoma.
- Explain how Hedgehog pathway activation drives basal cell carcinoma and why it rarely metastasises.
- Explain what grade and stage measure in keratinocyte cancers, and outline Merkel cell carcinoma.
What it is
Non-melanocytic skin tumours arise from the epidermis and its appendages rather than from melanocytes. The large group are tumours of keratinocytes: benign (seborrhoeic keratosis), dysplastic precursors (actinic keratosis, squamous cell carcinoma in situ) and the two commonest human cancers, basal cell carcinoma and cutaneous squamous cell carcinoma, together called keratinocyte carcinomas. Rarer tumours include Merkel cell carcinoma and adnexal tumours.
4 types to tell apart
- Benign keratinocyte tumours
- Seborrhoeic keratosis: uniform basal-like cells with horn cysts, no atypia, not a precursor of carcinoma.
- Squamous precursors
- Actinic keratosis (atypia in the lower epidermis) and Bowen disease (squamous cell carcinoma in situ, atypia through the full thickness).
- Keratinocyte carcinomas
- Basal cell carcinoma (Hedgehog-driven, locally invasive, rarely metastasises) and cutaneous squamous cell carcinoma (can reach lymph nodes); keratoacanthoma is usually regarded as a variant of well-differentiated squamous cell carcinoma.
- Merkel cell carcinoma
- A rare, aggressive neuroendocrine carcinoma, mostly driven by Merkel cell polyomavirus, otherwise by ultraviolet damage.
US spelling: tumours → tumors, tumour → tumor.
Normal function
The epidermis: keratinocytes renewed from the basal layer
The epidermis is a keratinising stratified squamous epithelium made mostly of keratinocytes. Stem cells in the divide; their daughters rise through the , joined by desmosomes, and the , then die and flatten into the and are shed, a journey of about a month. Stem cells in the hair follicle can also renew the epidermis.
Among the basal cells sit melanocytes (their tumours have their own lesson) and Merkel cells, touch receptors with neuroendocrine granules. Below the basement membrane, the holds the capillaries and lymphatics an invasive tumour would need to reach.
Melanin over keratinocyte nuclei absorbs ultraviolet (UV) light, and badly damaged keratinocytes normally die by apoptosis under the control of p53. Skin cancers arise when this protection is overwhelmed over decades.
Underlying change · Step 1 of 5
Ultraviolet light writes its signature in keratinocyte DNA
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 9 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Underlying change · Step 2 of 5
Seborrhoeic and actinic keratoses, and Bowen disease
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 9 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Disrupted function · Step 3 of 5
Cutaneous squamous cell carcinoma: through the basement membrane
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 9 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Disrupted function · Step 4 of 5
Basal cell carcinoma: Hedgehog-driven and locally destructive
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 9 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Consequences · Step 5 of 5
Spread, what staging measures, and Merkel cell carcinoma
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 9 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Symptoms and signs
Symptoms, signs and findings
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 9 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Recap
Recap
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 9 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Self-check
Check your understanding
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 9 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .