Question about PET/CT scans

Trillion · New User Joined: 19 Aug 2009 Posts: 4

I recently was diagnosed with Melanoma and went to have a SNB. Because my signal nodes were in unusual places requiring much more complicated surgery than expected, my surgeon elected to cancel the SNB and referred me to another surgeon who specializes in these sorts of things. He is a busy man and I was not able to get an appointment until next Tuesday, 8/25. In the meantime my original surgeon, after discussing my case with an oncologist, decided it would be a good idea for me to get a PET/CT scan before seeing the new surgeon. I did get the scan and it came back completely negative which was fantastic given my melanoma was 2.6mm and ulcerated!

Here's my question -- Does a PET/CT scan show cancer in the lymph system and if so, what would be the purpose of a SNB at this point?

HaoleBoy · Senior User Joined: 19 Aug 2008 Posts: 108

Trillion, you absolutely need to go on and get the SNB -- particularly with a primary tumor that measured 2.60 mm Breslow thickness and was ulcerated....The short answer is "no", a PET/CT scan will not detect melanoma metastases in the lymphatic system....The longer answer follows...

The PET/CT scan is good for picking up metabolically active macro-disease -- particularly macro-level distant spread to an organ.... but PET/CT scans do have a minimum threshold... I want to say the lesion has to be about 4mm in size before PET/CT will detect it but don't quote me on that (or about 1/6 inch)...

The SNB will identify what is called occult (hidden) microscopic level disease in the sentinel lymph node(s)....The difference in the order of magnitude for a SNB is thus:

a. Histological stain (basically a quick screen) will identify 1 melanoma CELL in a background of 10,000 healthy cells..

b. The subsequent immunohistochemical stain will identify 1 melanoma CELL in a sentinel node biopsy in a background of 100,000 healthy cells...

So the difference is basically between something about 1/6 of an inch (PET/CT) versus sub-microscopic in size (SNB).... You need to realize that one of the things which makes melanoma so damn deadly when not caught early (meaning before the tumor exceeds 1mm in thickness or metastisizes) is that basically most melanoma cells are clonal -- meaning they have the potential to generate a metastasis whereas other cancer tumors only have 1 out of 55 or so malignant cells able to spawn a metastasis.....And the outlook for metastatic melanoma is not very good since the adjuvant systemic treatment drugs basically suck in terms of overall response rates and complete response rates -- although there are some promising trials (but even here, a 35 % complete response is not too common)...

The SNB can be a life saving procedure because even if the stains don't detect even a super sub-microscopic malignant cell ...By removing the sentinel node(s), it removes occult (hidden) disease before it has the opportunity to grow into clinical disease and spread elsewhere....

If you are in the US, the SNB is "standard of care" for melanoma over 1mm in thickness (and even thinner when ulcerated)...

I don't want to scare you, but you will be playing Russian Roulette with several rounds in the chamber if you forego the SNB.....It is a good thing that you were referred to a specialist.... There is both a nuclear medicine and a surgical oncology learning curve involved with the SNB procedure -- i.e., the possibility of a SNB mapping and surgical error in performing the procedure which could lead to either not identifying the "true" sentinel node -- which would lead to a false negative -- or in contaminating the SNB surgical field with a possible malignant node... Conventional wisdom is that most surgical oncologists need to perform 35 or more SNBs to be proficient in the procedure....My surgical oncologist at a US NCI designated Comprehensive Cancer Center had performed over 1000+ SNBs when he did mine, and he teaches/mentors younger Surgical Oncologist "wannabes" in the procedure....

Trillion, best of luck to you and God Bless,

HaoleBoy (aka Hawaii Bob)
Stage IIA
2.40mm Primary Tumor bottom of left foot 2nd toe (amputated in WLE)
SNB (left femoral groin) Negative for Melanoma
21 August 2008
1 Year No Evidence of Desease (NED) TODAY (I hope)

Trillion · New User Joined: 19 Aug 2009 Posts: 4

Thank you so much for the thorough answer. It was exactly the information I needed to know. As I'm sure you guessed, I am weighing the risks/benefits of the SNB given that my SNB surgery will be more complicated than many. The melanoma was in my calf and they found nodes in the groin, pelvic and stomach areas.

The bad news from your post is that basically the PET/CT only tells me I don't have tumors large enough to be seen, not that they don't exist. I'll try to keep my positive face on and hope there really aren't any.

HaoleBoy · Senior User Joined: 19 Aug 2008 Posts: 108

Trillion, are you in the U.S.A ? If so, I would encourage you to go to a U.S. National Cancer Institute designated Comprehensive Cancer Center and see a Surgical Oncologist who specializes in melanoma ....

I presume you haven't had the Wide Local Excision yet ? or did you ? (the two procedures should be done sequentially right after one another while you're under anesthesia).... It sounds like they did at least perform the Sentinel Lymph Node mapping -- which is normally done before a patient goes into pre-op (or at most a day or two before the WLE/SNB)...

While anything is possible I guess, I've never heard of anyone with a lower extremity melanoma having sentinel nodes other than behind the knee or in the femoral groin, thus my questions -- I kinda suspect that there may have been a mapping error but, in a very low percentage of cases (about 1 - 3 %) -- mostly involving primary tumors around the head and neck region which can drain to at least 3 different regional lymph node basins -- the nuclear medicine folks aren't able to find the sentinel node.

If you are in the U.S.A and need any assistance in finding a Melanoma Center of Excellence, I strongly recommend that you visit Catherine Poole's website Melanoma International Foundation at the URL below. Catherine is a professional melanoma patient advocate, a melanoma survivor herself, and is very well wired into the American melanoma Centers of Excellence throughout the U.S. .... She is also a very helpful and caring person who helped me out big time when I was diagnosed....

Trillion, after you go through the WLE/SNB, you may want to have a conversation about Interferon follow-on treatment -- there are a lot of pros and cons, but there was a European study presented at last June's American Society of Clinical Oncologists' 2009 Annual Meeting which concluded that interferon adjuvant treatment was -- for some reason -- much more effective in delaying/preventing disease recurrence in patients with ulcerated melanomas than in patients with non-ulcerated melanomas... I posted the abstract to this study in Cancer Forums and you may want to read it later on after your treatment (but note that the dosage protocols were different in the European study compared to the protocol in the U.S.)..... but first things first....

Trillion, Wishing you the best for successful treatment and a speedy recovery... and kudos to you for the positive attitude...

Aloha, HaoleBoy (aka Hawaii Bob on other forums)

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