For many years the invasive and potentially uneccesary surgical procedure sentinel node biopsy has formed the mainstay of nodal staging of melanoma. It is an effective tool for the detection of metastases (tumour spread) to lymphatic drainage basins to the extent that even microscopic deposits are detected during laboratory tissue analysis. Herein lies one of the problems, since these so-called micrometastases are something of an unknown entity. Not all microscopic deposits may lead to palpable tumours as the body’s own immune system has the capacity to fight the spread of melanoma to some extent. The sentinel node biopsy procedure is also a fairly major surgical procedure and is not without unpleasant and potentially harmful side effects.
Advances in ultrasound since its entrance into clinical practice in the 1980s have been considerable. Modern high resolution ultrasound machines (typically scanning at 18MHz) combine excellent spatial and contrast resolution on soft tissues which are readily accessible with a surface probe. The skin and underlying superficial tissues and blood vessels are amenable to ultrasound examination.
With the most modern machines, sub-millimetre resolution is achievable meaning that very small melanoma metastases which are not (yet) palpable to the surgeon’s hand can be detected. In specialist units equipped with on site cytology specialists, fine needle aspiration can be performed allowing cellular grade diagnosis from a targeted minimally invasive procedure which is no more traumatic than a blood test.
These new methods have not yet been validated against clinical examination and sentinel node biopsy, but several major centres in Europe are currently trialling these methods.
Dr Christiane Voit of Charité Hospital, Berlin is regarded as a pioneer in the use of ultrasound in melanoma and published The Rotterdam Criteria for assessment of sentinel nodes.
Professor J Meirion Thomas has recently launched a trial in the UK (SUNMEL) which aims to test ultrasound surveillance against more established methods.