› Forums › General Melanoma Community › PET CT and minimum tumor size
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CHD.
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- July 7, 2015 at 4:10 pm
Does anyone know whether a 2 x 3 cm superficial spreading melanoma would show up on a PET CT or plain CT?
I always think of these questions right after appointments, with another 3 months before I go back in.
My last PET CT was clear, but I got to wondering: If superficial spreading melanoma spread internally, how big would it have to be to show up on PET? Unless it took a more nodular form, it seems like it could grow for awhile before being detectable.
Would it even show up at all on a regular CT scan?
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- July 7, 2015 at 6:07 pm
I was told 5 millimeters. Sometimes even a little smaller but that is what I was told. 2 x 3 cm could definitely be seen.
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- July 7, 2015 at 8:18 pm
CTs often have different "slice" resolutions – they can see more or less depending on the slice size. Sometimes tumors are small enough to fit between the slices or only show a small amount in a single slice. It's like looking for a raisin inside a piece of cake – depends on how you slice it! You could cut 1" slices and still not see that raisin if it fell exactly between two slices. PET scans minimum resolution is around 5mm. CT scans may be a little better depending upon the resolution.
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- July 7, 2015 at 8:18 pm
CTs often have different "slice" resolutions – they can see more or less depending on the slice size. Sometimes tumors are small enough to fit between the slices or only show a small amount in a single slice. It's like looking for a raisin inside a piece of cake – depends on how you slice it! You could cut 1" slices and still not see that raisin if it fell exactly between two slices. PET scans minimum resolution is around 5mm. CT scans may be a little better depending upon the resolution.
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- July 7, 2015 at 8:18 pm
CTs often have different "slice" resolutions – they can see more or less depending on the slice size. Sometimes tumors are small enough to fit between the slices or only show a small amount in a single slice. It's like looking for a raisin inside a piece of cake – depends on how you slice it! You could cut 1" slices and still not see that raisin if it fell exactly between two slices. PET scans minimum resolution is around 5mm. CT scans may be a little better depending upon the resolution.
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- July 8, 2015 at 1:54 pm
Thanks for the replies! I feel like I have a much better understanding of how PET CT works. I think next time I see my doc I will ask whether metastatic melanoma is always nodular, even if starts out superficial spreading type. I am on the lookout for new superficial spreading type primaries or local recurrences, but now I wonder whether it would also spread that way internally. If so, it grows so slowly it seems like it could evade detection for quite awhile. Everyone I know personally with melanoma has nodular type. Anyway, I'm just curious how it works.
Thanks again!
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- July 8, 2015 at 1:54 pm
Thanks for the replies! I feel like I have a much better understanding of how PET CT works. I think next time I see my doc I will ask whether metastatic melanoma is always nodular, even if starts out superficial spreading type. I am on the lookout for new superficial spreading type primaries or local recurrences, but now I wonder whether it would also spread that way internally. If so, it grows so slowly it seems like it could evade detection for quite awhile. Everyone I know personally with melanoma has nodular type. Anyway, I'm just curious how it works.
Thanks again!
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- July 8, 2015 at 2:11 pm
It spreads cell by cell, not tumor by tumor. So once it is in the lymph or blood stream, no one cares if the original tumor was superficial spreading or nodular. It is metastatic now. Metastatic tumors are not categorized as "acral", "SSM", "LMM" or nodular, they are melanoma. It's only the primary that has this designation.
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- July 8, 2015 at 2:11 pm
It spreads cell by cell, not tumor by tumor. So once it is in the lymph or blood stream, no one cares if the original tumor was superficial spreading or nodular. It is metastatic now. Metastatic tumors are not categorized as "acral", "SSM", "LMM" or nodular, they are melanoma. It's only the primary that has this designation.
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- July 8, 2015 at 3:27 pm
There is no similarity, no designation of tumor shape and size or ANYTHING that relates back to the original primary designation. The tumor grows uncontrolled – basically the definition of a tumor. It may grow fast or slow, but rarely is that related to the original tumor type. The one exception may be desmoplastic melanoma. That one type seems to have slower tumor growth characteristics. Slower growth, but nothing relating to the size/shape of the tumor. But since that isn't your type of melanoma, it isn't relevant.
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- July 8, 2015 at 3:27 pm
There is no similarity, no designation of tumor shape and size or ANYTHING that relates back to the original primary designation. The tumor grows uncontrolled – basically the definition of a tumor. It may grow fast or slow, but rarely is that related to the original tumor type. The one exception may be desmoplastic melanoma. That one type seems to have slower tumor growth characteristics. Slower growth, but nothing relating to the size/shape of the tumor. But since that isn't your type of melanoma, it isn't relevant.
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- July 8, 2015 at 4:11 pm
So then once melanoma cells have entered the blood stream and begin to metastasize, they basically form tumors, period. No difference based on primary. To clarify, I am thinking the tumors might vary based on location, so that a bone tumor might appear different than an adrenal gland tumor, but it is unrelated to the way the primary appeared. Basically, melanoma tumors are melanoma tumors regardless of how they started, the only differences among us being in the genetic mutations, mitotic rates, etc.
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- July 8, 2015 at 4:59 pm
OK, got it. I had been wondering if a completely flat, internal superficial spreading melanoma might be missed on a scan, or might spread all over before anyone even knew it was there, and this has completely changed my thinking on how it all works. It is actually reassuring. It is interesting and seems almost counterintuitive that the appearance it takes on the skin will tend to be consistent with multiple primaries or local recurrences, but once it goes internal, the tumors it forms are not.
The info on how the PET CT works is appreciated too.
Thank you!
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- July 8, 2015 at 4:59 pm
OK, got it. I had been wondering if a completely flat, internal superficial spreading melanoma might be missed on a scan, or might spread all over before anyone even knew it was there, and this has completely changed my thinking on how it all works. It is actually reassuring. It is interesting and seems almost counterintuitive that the appearance it takes on the skin will tend to be consistent with multiple primaries or local recurrences, but once it goes internal, the tumors it forms are not.
The info on how the PET CT works is appreciated too.
Thank you!
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- July 9, 2015 at 12:47 am
Melanoma in situ might be flat, but even SSM grows vertically into the skin. Nodular may grow faster than the other types, but when it comes down to it – all types have a vertical growth phase. That's how the cells find the lymph and blood vessels. There are two growth phases, radial and vertical. The initial characteristics about how the melanoma cells interact with skin cells may vary some in their growth patterns and rate of growth, but they all do their thing when they go to other body locations. They all create a skin tumor first to some extent, then try to make one elsewhere in the body if possible.
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- July 9, 2015 at 12:47 am
Melanoma in situ might be flat, but even SSM grows vertically into the skin. Nodular may grow faster than the other types, but when it comes down to it – all types have a vertical growth phase. That's how the cells find the lymph and blood vessels. There are two growth phases, radial and vertical. The initial characteristics about how the melanoma cells interact with skin cells may vary some in their growth patterns and rate of growth, but they all do their thing when they go to other body locations. They all create a skin tumor first to some extent, then try to make one elsewhere in the body if possible.
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- July 9, 2015 at 12:47 am
Melanoma in situ might be flat, but even SSM grows vertically into the skin. Nodular may grow faster than the other types, but when it comes down to it – all types have a vertical growth phase. That's how the cells find the lymph and blood vessels. There are two growth phases, radial and vertical. The initial characteristics about how the melanoma cells interact with skin cells may vary some in their growth patterns and rate of growth, but they all do their thing when they go to other body locations. They all create a skin tumor first to some extent, then try to make one elsewhere in the body if possible.
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- July 9, 2015 at 2:08 am
That's so true, even SSM has the vertical phase. Where I got hung up was thinking that if SSM spread, it would create another SSM somewhere else, whether on the skin or inside the body. Nodular would create more nodular, amelanotic would create more amelanotic… no matter where it formed. So I had been thinking that a nodular tumor would be obviously much easier to spot on a routine CT than a mostly flat, horizontally spread out SSM, even if it had grown somewhat vertically.
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- July 9, 2015 at 2:27 am
One more clarification. A new SSM on the skin is a new PRIMARY and not related to your first one. It's a unique occurrence. If it were a recurrence from your first primary, it grows from the lymph vessels up into the skin, not from the top down. It would essentially be subcutaneous even though it might eventually show some evidence on the skin.
In the end, regardless of the manifestation on the skin, all melanoma is melanocytes gone bad. It's still one type of cell no matter where it goes.
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- July 9, 2015 at 4:35 pm
This makes me wonder what a SSM growing from the lymph vessels up into the skin would look like compared to one growing top down. If the same, then I wonder if it would even be possible to tell except to examine it microscopically? By definition, a melanoma in situ, even if found near the primary, would have to be a new primary then, if I understand this correctly, based on the fact that it is limited to the surface of the skin.
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- July 9, 2015 at 4:55 pm
Subcutaneous lesions don't often have an epidermal component. Growth patterns typically make it easy to determine "primary" versus metastasis. Most mets would NOT look like primaries – many are lumps under the skin. May be black, may be skin colored. I really don't think you need to worry about either! But if you see something on the skin that reminds you of your in situ, biopsy it. It's more likely to be a new primary than a met.
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- July 9, 2015 at 5:17 pm
I actually never saw my in situ, it was found on pathology, long story. But my primary was NOT in situ (I only wish). This just made me realize that I had been assuming the in situ was related to my primary since it was nearby, and it couldn't have been since it was in situ. The only thing I have seen was my primary, which again was an SSM, about 2 x 3 cm, flat, deeply pigmented, multicolored, and pretty classic for SSM. But whenever I imagined an internal metastasis, I envisioned exactly the same type of lesion appearing on an internal organ. It is also what I have been on the lookout for on my skin, something identical to my primary. So this has been very helpful to me and I appreciate it.
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- July 9, 2015 at 5:17 pm
I actually never saw my in situ, it was found on pathology, long story. But my primary was NOT in situ (I only wish). This just made me realize that I had been assuming the in situ was related to my primary since it was nearby, and it couldn't have been since it was in situ. The only thing I have seen was my primary, which again was an SSM, about 2 x 3 cm, flat, deeply pigmented, multicolored, and pretty classic for SSM. But whenever I imagined an internal metastasis, I envisioned exactly the same type of lesion appearing on an internal organ. It is also what I have been on the lookout for on my skin, something identical to my primary. So this has been very helpful to me and I appreciate it.
-
- July 9, 2015 at 5:17 pm
I actually never saw my in situ, it was found on pathology, long story. But my primary was NOT in situ (I only wish). This just made me realize that I had been assuming the in situ was related to my primary since it was nearby, and it couldn't have been since it was in situ. The only thing I have seen was my primary, which again was an SSM, about 2 x 3 cm, flat, deeply pigmented, multicolored, and pretty classic for SSM. But whenever I imagined an internal metastasis, I envisioned exactly the same type of lesion appearing on an internal organ. It is also what I have been on the lookout for on my skin, something identical to my primary. So this has been very helpful to me and I appreciate it.
-
- July 9, 2015 at 4:55 pm
Subcutaneous lesions don't often have an epidermal component. Growth patterns typically make it easy to determine "primary" versus metastasis. Most mets would NOT look like primaries – many are lumps under the skin. May be black, may be skin colored. I really don't think you need to worry about either! But if you see something on the skin that reminds you of your in situ, biopsy it. It's more likely to be a new primary than a met.
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- July 9, 2015 at 4:55 pm
Subcutaneous lesions don't often have an epidermal component. Growth patterns typically make it easy to determine "primary" versus metastasis. Most mets would NOT look like primaries – many are lumps under the skin. May be black, may be skin colored. I really don't think you need to worry about either! But if you see something on the skin that reminds you of your in situ, biopsy it. It's more likely to be a new primary than a met.
-
- July 9, 2015 at 4:35 pm
This makes me wonder what a SSM growing from the lymph vessels up into the skin would look like compared to one growing top down. If the same, then I wonder if it would even be possible to tell except to examine it microscopically? By definition, a melanoma in situ, even if found near the primary, would have to be a new primary then, if I understand this correctly, based on the fact that it is limited to the surface of the skin.
-
- July 9, 2015 at 4:35 pm
This makes me wonder what a SSM growing from the lymph vessels up into the skin would look like compared to one growing top down. If the same, then I wonder if it would even be possible to tell except to examine it microscopically? By definition, a melanoma in situ, even if found near the primary, would have to be a new primary then, if I understand this correctly, based on the fact that it is limited to the surface of the skin.
-
- July 9, 2015 at 2:27 am
One more clarification. A new SSM on the skin is a new PRIMARY and not related to your first one. It's a unique occurrence. If it were a recurrence from your first primary, it grows from the lymph vessels up into the skin, not from the top down. It would essentially be subcutaneous even though it might eventually show some evidence on the skin.
In the end, regardless of the manifestation on the skin, all melanoma is melanocytes gone bad. It's still one type of cell no matter where it goes.
-
- July 9, 2015 at 2:27 am
One more clarification. A new SSM on the skin is a new PRIMARY and not related to your first one. It's a unique occurrence. If it were a recurrence from your first primary, it grows from the lymph vessels up into the skin, not from the top down. It would essentially be subcutaneous even though it might eventually show some evidence on the skin.
In the end, regardless of the manifestation on the skin, all melanoma is melanocytes gone bad. It's still one type of cell no matter where it goes.
-
- July 9, 2015 at 2:08 am
That's so true, even SSM has the vertical phase. Where I got hung up was thinking that if SSM spread, it would create another SSM somewhere else, whether on the skin or inside the body. Nodular would create more nodular, amelanotic would create more amelanotic… no matter where it formed. So I had been thinking that a nodular tumor would be obviously much easier to spot on a routine CT than a mostly flat, horizontally spread out SSM, even if it had grown somewhat vertically.
-
- July 9, 2015 at 2:08 am
That's so true, even SSM has the vertical phase. Where I got hung up was thinking that if SSM spread, it would create another SSM somewhere else, whether on the skin or inside the body. Nodular would create more nodular, amelanotic would create more amelanotic… no matter where it formed. So I had been thinking that a nodular tumor would be obviously much easier to spot on a routine CT than a mostly flat, horizontally spread out SSM, even if it had grown somewhat vertically.
-
- July 8, 2015 at 4:59 pm
OK, got it. I had been wondering if a completely flat, internal superficial spreading melanoma might be missed on a scan, or might spread all over before anyone even knew it was there, and this has completely changed my thinking on how it all works. It is actually reassuring. It is interesting and seems almost counterintuitive that the appearance it takes on the skin will tend to be consistent with multiple primaries or local recurrences, but once it goes internal, the tumors it forms are not.
The info on how the PET CT works is appreciated too.
Thank you!
-
- July 8, 2015 at 4:11 pm
So then once melanoma cells have entered the blood stream and begin to metastasize, they basically form tumors, period. No difference based on primary. To clarify, I am thinking the tumors might vary based on location, so that a bone tumor might appear different than an adrenal gland tumor, but it is unrelated to the way the primary appeared. Basically, melanoma tumors are melanoma tumors regardless of how they started, the only differences among us being in the genetic mutations, mitotic rates, etc.
-
- July 8, 2015 at 4:11 pm
So then once melanoma cells have entered the blood stream and begin to metastasize, they basically form tumors, period. No difference based on primary. To clarify, I am thinking the tumors might vary based on location, so that a bone tumor might appear different than an adrenal gland tumor, but it is unrelated to the way the primary appeared. Basically, melanoma tumors are melanoma tumors regardless of how they started, the only differences among us being in the genetic mutations, mitotic rates, etc.
-
- July 8, 2015 at 3:27 pm
There is no similarity, no designation of tumor shape and size or ANYTHING that relates back to the original primary designation. The tumor grows uncontrolled – basically the definition of a tumor. It may grow fast or slow, but rarely is that related to the original tumor type. The one exception may be desmoplastic melanoma. That one type seems to have slower tumor growth characteristics. Slower growth, but nothing relating to the size/shape of the tumor. But since that isn't your type of melanoma, it isn't relevant.
-
- July 8, 2015 at 2:11 pm
It spreads cell by cell, not tumor by tumor. So once it is in the lymph or blood stream, no one cares if the original tumor was superficial spreading or nodular. It is metastatic now. Metastatic tumors are not categorized as "acral", "SSM", "LMM" or nodular, they are melanoma. It's only the primary that has this designation.
-
- July 8, 2015 at 1:54 pm
Thanks for the replies! I feel like I have a much better understanding of how PET CT works. I think next time I see my doc I will ask whether metastatic melanoma is always nodular, even if starts out superficial spreading type. I am on the lookout for new superficial spreading type primaries or local recurrences, but now I wonder whether it would also spread that way internally. If so, it grows so slowly it seems like it could evade detection for quite awhile. Everyone I know personally with melanoma has nodular type. Anyway, I'm just curious how it works.
Thanks again!
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Tagged: cutaneous melanoma
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