@dave62 As much as we as patients want clear cut answers, sometimes those answers come as a reduction of risk rather than an absolute answer. Doctors can't give us an absolute promise that there will never be another cancer re-occurrence, but we do have choices that can lower our risks. There are many studies on melanoma cancer in regard to the size and depth of a lesion and the mortality statistics in relation to the size of the excision margins. I am not a medical professional and don't have the training to advise your best course of action. I did look up some studies and found this:

Quoted from this link about sentinal lymph node biopsy " SLNB" which does support yours at .7mm as borderline
https://emedicine.medscape.com/article/854424-overview
"Indications for SLNB
SLNB should not be offered for melanoma in situ, where the cancer cells are confined to the epidermis.
SLNB should not be recommended routinely for thin melanomas that are T1a (nonulcerated lesions < 0.8 mm Breslow thickness).
SLNB should be considered for thin melanomas that are T1b (0.8 to 1-mm thickness or < 0.8 mm with ulceration).
SLNB should be recommended to patients with a clinically negative nodal basin and intermediate thickness primary melanomas (T2 or T3; >1 mm to 4 mm).
SLNB should be considered for thick melanomas (T4; >4 mm) and clinically negative nodes.
SLNB may be considered for melanoma that exhibits regression (controversial).
Potential contraindications for SLNB
SLNB is unnecessary if systemic disease is present.
SLNB may not be reliable if there has been previous extensive surgery in the targeted lymph node basin."

Quoted from this link about excision margin size:
https://link.springer.com/article/10.1245/s10434-015-4950-0
"Simply stated, for melanomas <and> 2 mm, 1-cm and 2-cm margins respectively appear to be wide enough, with still some lingering uncertainty about the appropriate margin in 1- to 2-mm subgroup"

As the spouse of a patient with a melanoma that was close to 7 mm in diameter (pencil eraser size), I worried too. I can't specifically remember the depth, but it was around 4mm and the biopsy done by the dermatologist did not get all the margins. The dermatologist sent him to a surgical oncologist and his surgery and skin graft was done at the hospital. Perhaps that is standard when a sentinal lymph node study is required. I looked up his notes and they said it was a 1 cm excision size around the lesion. They took all the skin layers right down to muscle and bone, and the resulting skin graft is about an inch and a quarter in diameter on his hand. I really don't think of him as being different after this, but because we have the knowledge that he is a high cancer risk because of the Castle test, we know that for the rest of his life, frequent visits to the dermatologist are necessary to catch any skin issues right away. Still, there is the risk of melanoma occurring internally or some other kind of cancer. There was no evidence of any spread on the pathology report, so there was no further treatment beyond surgery needed. He was offered a study if he wanted to pursue an IV cancer drug to be administered at stage 2. It would be standard treatment if this was stage 3. He decided against it because of needing to drive to downtown Chicago to participate and right when the pandemic was starting with the risk of crowded facilities and people all around us. I do also have a friend who had melanoma taken off her leg twenty years ago, and has never had another problem with it since, so that is good news that this can be cured and over with the help of a surgeon and timely intervention. It all comes down to advocating for yourself and getting suspicious growths checked out early. My husband had melanoma on his hand for a year thinking it was a wart. That was a serous mistake, but it seems that it was caught in time. We don't have any family data to rely on as he is adopted, but the Castle test indicated a genetic risk of cancer.

Here is the Castle lab information. Do you think this could help you with your decisions?
https://castlebiosciences.com/