Skin oncology Flashcards
What are the two types of skin cancers
Non melanoma
Melanoma
What are the risk factors of skin cancer
UV radiation, exposure to ionizing radiation, immunosuppression, inherited disorders, chemical exposure, chronic irritation
What are the inherited disorders of skin cancer
Xeroderma pigmentosum
Epidermolysis bullosa
Albinism
Basal cell neveus syndrome (gorlin’s syndome)
What is the high risk region
H zone : embryonal fusion planes where cancers can infiltrate deeply
What are the histopathologies of skin cancer
Basal cell carcinoma 65%
Squamous cell carcinoma 35%
Melanoma 1-2%
Name the layers of the epidermis from superficial to deep
Corneum (squames)
Granulosum (keratohyalin granules)
Spinosum (desmosomes)
Basale (germinal)
Examples of premalignant lesions
Actinic keratosis
Bowens disease
Keratocanthoma
What is each premalignant lesion’s likleyhood of progression to SCC
Actinic keratosis: 1-20%
Bowen’s disease: 3-5%
How long is the dermis and what does it contain
1-2 mm
- lymphatics, nerves, connective tissue, blood vessels, and sweat glands
What are the layers of the skin
Epidermis, dermis, subcutaneous tissue
What are the treatment options for actinic keratosis
- cryotherapy
- curettage
- topical 5 FU
How does keratoacanthoma progress
Grows rapidly for 1-2 months then involutes by 3-6 months spontaneously
What is the treatment for keratocanthoma
Surgery
What does ABCDE stand for in detection for early melanoma
Asymmetry, borders , colour, diameter, evolving
What percentage of basal cell carcinoma occur on face
70%
What are the clinical presentations of basal cell carcinoma and each of their percentages
Nodular: 50-60%
Superficial: 30%
Morpheaform / sclerosing : 5-10%
What are the rare histologies for basal cell carcinoma
- micronodular
- infiltrating
- basilosquamous
- keratosis
Describe the appearance of nodular BCC / ulcerative
Pearly
Central ulceration
Heaped up boarders
Translucent
Describe the appearance of superficial BCC
Scaley macules with indistinct margin
Describe the appearance of morphia form / sclerosing BCC
- flat, indurated ill defined macule with shiny surface that become depressed as they grow . Whitish firm plaque with somewhat distinct margins
Describe the appearance of a solitary lesion
- bright red lesion
- detected with side lighting
What is the treatment for keloids
Surgically with radiotherapy
What is the percentage of recurrence with keloids without radiotherapy
50-80%
What is the treatment procedure regime for keloids
- 2cm margin around the new scar
- 800 cry x 2 with two days in between
What are examples of management of non melanoma skin cancers
- cryotherapy
- electrosurgery
- topical treatment
- radiation therapy
- Moh’s surgery
- surgical resection
What are the advantages and disadvantage of cryotherapy
- quick
- cost effective
- excellent cosmetic result
- no anathema required
- high cure rate for appropriate indications
- well tolerated by patients
Disadvantage: no histology confirmation of margins
Describe the treatment for melanoma
- wide local excision for primary tumours
- lymph node assessment if indicated
- radiotherapy for palliation (since it is radioresistant)
- systemic therapy (immunotherapy)
What is the stand off effect
Distance between patient skin and applicator/cone that results in significant dose fall off depending on the size of the tumour. Lesion is below the skin surface
How do we compensate for the standoff effect
- Compensator
- Increase SSD
Describe the difference between positive and negative stand off
Positive : lesion is below the surface of the skin and SSD is longer. Decrease dose rate at the surface
Negative : lesion is above the surface of the skin and SSD is shower.
What are some solutions to the standoff effect
- Changing prescription point
- Using compensating filter such as aluminum or foil (more)
- Using extended SSD (but increases treatment time)
What are the advantages and disadvantages of Moh’s surgery
- high cure rate > 90%
- spares normal tissue
- dis: more time consuming and expensive
When is Mohl’s surgery used
Primary or recurrent SCC and BCC with high risk features
How do you increase electron beam surface dose
Use a bonus of 0.5-1cm (decreases dose at depth)
Use a tantalum mesh (dose not affect dose at depth)
Characteristics of electron beams
- low energy electrons ; Isidore curves show some bulging
- high energy electron: isotope curves constrict
- surface dose increases as energy increases
What are the advantages of electron treatment
- direct energy deposition as they travel through the medium
- rapid dose fall off, dose is deposited at the surface
- minimal dose deposited at depth (end of practical range)
- more homogenous distribution over a large diameter tumour (greater than 8-10cm)
What are the advantages of electron treatment
- direct energy deposition as they travel through the medium
- rapid dose fall off, dose is deposited at the surface
- minimal dose deposited at depth (end of practical range)
- more homogenous distribution over a large diameter tumour (greater than 8-10cm)
How big is electron penumbra and when does it increase
- about 1 cm
- decreased electron beam energy
- increased field size
- increase distance from applicator
What are common dosage fractionations
35gy in 7 fractions
45gy in 10 fractions
50gy in 20 fractions
What are the characteristics of orthovoltage
- low energy x ray
- 75-300 kv
- 100% surface dose
- narrow penumbra (1-3mm)
- easy to shield
What are the diagnostic procedures for BCC SCC and melanoma
History and physical
Biopsy
What are the staging tests for SCC and melanoma
BCC (unlikely)
SCC - full dermatologic exam and palpation of draining LNs
Melanoma - sentinel LN, U/S of LNs
TNM staging for BCC and SCC
T : size and extent/invasion
N: size, number and location (ipsilateral and contralateral)
M : presence or absence of distant Mets
TNM staging of melanoma
T: tumour thickness and b sub staging refers to ulceration
N: number of lymph nodes
M: sub divided into M1a, M1b, M1c
What is the primary treatment for ALL skin cancers (BCC, SCC, melanoma)
Surgery
What are the radiation doses for BCC and SCC
35/7 , 45/10, 50/20
But also dependant on location depth and size
Role of systemic therapy in BCC and SCC
Not used - unlikley that it has gone beyond regional lymphnodes
What is the role of radiotherapy in BCC and SCC
- adjuvant
- definitive (primary)
Depends on patient factor and tumour factors
What is the role of radiation therapy in melanoma
- palliative (since it is radioresistant)
- or extra coal spread, large nodes, > 3 LNs, cervical nodes
What is the typical dose for melanoma
50/25
What is the dosage for keloids
- 16 Gy / 2 fx with 2 days apart (the day after surgery)
What is the percentage of recurrence of keloids after surgery
50-80%
What is the F factor
Value used to calculate dose in any material from exposure that is measured in air
(Mass energy coefficient for the material divided by the mass energy coefficient for air)
What is the clinical implication of F factor
Bone absorbs more dose with orthovoltage treatment which raises theoretical risk of development of osteoradionecrosis (severe bone damage)
What does F factor depend on
Size of field and previous irradiation
Where do constrictions and bulging out occur at the isodose lines
< 70 %, < 50%
What is the rate at which electrons lose energy
2 MeV / cm
How do you calculate the minimum thickness of lead required for adequate blocking (5% transmission)
= Energy (in MV) / 2
