"What's this doc?" - Using Punch Biopsy to Diagnose Skin Cancer | What to Expect?
"What's this doc?" the patient asks, edging closer with their show and tell opportunity as the skin feature comes into my view.
This is a very common question I get numerous times a week during skin checks as patients recount their carefree and youthful days of sunburnt bliss. Especially for my older patients, ignorance of sun protection in their early years seemed universal, save for some zinc on the nose.
When we suspect a skin feature of being a cancer, sometimes the next appropriate step is to take a sample of this skin which can be sent to the laboratory and examined under a microscope. How do we begin going about this?
What is a Punch Biopsy?
In the mid-20th century, scientists started drilling ice cores from Antarctica to learn about past climate by analysing layers in the sample. The skin is likewise made of many different layers which may be affected by a potential cancer. The punch biopsy tool is a circular blade which is rotated with downward pressure to create a core of tissue, sampling all the skin layers in a column.
The procedure involves:
Cleaning the skin surface with an antiseptic such as iodine
Injection of local anaesthetic with a fine needle which can cause a stinging sensation.
The punch biopsy tool is used, allowing a sample to be taken using a pair of forceps and scalpel/scissors.
Bleeding is stopped with either firm pressure alone, or the use of sutures.
The sample is placed in a specimen jar and sent to the laboratory for analysis.
For those who are keen to see how this looks in practice, the following video from an Australian GP college (ACRRM) provides an overview of the procedure.
Things to Know Before the Biopsy
General risks of a punch biopsy are typical of most procedures that involve cutting the skin, including, but not limited to:
Pain: Usually tolerable and can be managed simply after the procedure with paracetamol
Swelling: Initial injection of local anaesthetics can cause initial swelling. Later swelling and redness can be a sign of infection.
Bleeding: Typically, bleeding is stopped before you leave the surgery! It is rare but possible for bleeding to occur in the hours following the procedure, though most minor bleeding can be stopped by applying firm pressure to the wound for 15+ minutes.
Dehiscence (splitting open of skin surface) if sutured: Unlikely given the small diameter and lower tension of punch biopsy wounds.
Infection: Redness, swelling or discharge at the wound site requires review.
Nerve damage: Punch biopsies should be superficial and care is taken to not damage underlying nerves.
Adverse reaction to antiseptic, local anaesthetics or adhesive from wound dressing: Alternative products can be considered if allergic or irritant reaction is known or encountered.
Scarring: Possibility for scarring as a spot (if not sutured) or a line (if sutured).
How to Care for the Wound after Punch Biopsy
The skin will slowly heal from bottom up, outside in. This is called healing by secondary intention.
Keep the wound dry for at least 24 hours, then the dressing may be changed once or twice a day.
The wound can be gently cleaned with soap and water then pat dry during dressing change.
Consider applying some petroleum jelly to the wound before covering with an adhesive bandage with non-stick gauze. Covering the wound helps with healing.
Keep the wound dry and covered under waterproof dressing for at least 1-2 days.
After removal of the waterproof dressing, the wound may be wet but not immersed with water.
Consider applying some petroleum jelly to promote wound healing and potentially reduce scarring. Maintaining adhesive bandage is optional.
Return after the agreed time period for removal of sutures.
Broader Reading: Beyond the Basics
The general principle of wound management is keeping the wound 'clean but greasy' to avoid drying it out. This is why petroleum jelly is traditionally recommended for scar minimisation of wounds.
However, there was a publicised study in 2018 showing that applying petroleum jelly too early can prevent the body from forming a natural plaster which can help wound healing. So perhaps delaying the application of petroleum jelly will achieve the best outcome.