0:00

So what do we do in the cases

0:02

where we don't see what we are expecting?

0:05

And so we're going to briefly stop here

0:07

and talk about PSMA negative disease

0:10

and we may encounter a scan that is negative when it,

0:13

we expect it to be positive in a whole bunch of reasons.

0:15

Um, but we need to keep in mind that 5%

0:17

of cases at diagnosis are going to be negative on PSMA pet.

0:21

So that's important to keep in mind.

0:23

So are we scanning the patient at a time of new diagnosis?

0:27

And if I don't see focal uptake in the prostate, I need

0:30

to confirm whether

0:31

or not the diagnosis

0:32

of prostate cancer has been established.

0:34

And I will be looking to see if there has been an MRI

0:37

to demonstrate there is a lesion of concern, PY RADS four,

0:40

PY RADS five and what the biopsy results showed.

0:43

If I don't see focal uptake in the prostate, it's okay

0:46

to say that and say, look,

0:47

there's no focal intense P SMA uptake in the prostate

0:50

to indicate a pre smma expressing lesion.

0:52

This raises concern for PSMA negative disease.

0:55

And then you know, you may choose

0:57

to add a disclaimer knowing

0:58

that this test will be less sensitive from um, nodal

1:00

and metastatic disease as well.

1:02

'cause you just may not see it.

1:03

A few haze times that I have seen this

1:05

and I don't see it all that often actually, um,

1:07

is unfortunately when you've got very high grade disease,

1:10

so Gleason nine where there may be a risk

1:12

of D differentiation or just very aggressive tumor

1:15

that isn't going to show up on PSMA

1:17

and depending on the clinical scenario,

1:19

I may recommend an FDG PET instead

1:21

to see if there is hypermetabolic disease

1:24

and then use FDG PET as the better modality to stage

1:28

for patients with biochemical recurrence or persistence.

1:30

However, it's a little bit of a different story

1:32

and often we're seeing patients

1:33

who have got really small rises in PSA, so we're looking at,

1:37

you know, 0.2 nanograms per liter, you know, really,

1:39

really small and we don't always see the recurrence.

1:43

Like PET is good but it's not perfect.

1:45

And so very small volume local recurrence may not be

1:48

apparent on our scan or it may be mixed in

1:50

with physiological uptake or in the range that's nonspecific

1:54

and we just are unable to call it.

1:56

So in those cases we would correlate with the PSA,

1:59

we would um, be guided by our referrers

2:02

and if the PSA does continue to rise,

2:04

they'll often be re imaged in three, six

2:06

or 12 months depending on the doubling time

2:08

and the risk associated with that.

2:11

But let's have a look at a patient

2:12

who's got widespread disease.

2:14

And I do have one case here and this patient had paired PSMA

2:17

and FDG PET cts and here are the two MIPS on the screen.

2:21

And you can see that on the PSMA pet, um,

2:24

that there is widespread skeletal metastatic disease

2:26

and it even on our FDG, there's heterogeneous uptake

2:30

through the skeleton as well

2:31

with some FDG expression within these lesions.

2:35

So this is a good example of

2:37

how you compare them side by side.

2:38

You know, potentially there is some lesions

2:40

that may be more hypermetabolic

2:42

and may be more amenable to different lines of therapy.

2:46

This is another case, um, similarly who,

2:49

where a patient had paired PSMA and FTG PET

2:52

and the patient was found to have liver lesions.

2:55

But interestingly these liver lesions were not particularly

2:59

Avid on the PSMA pet.

3:01

And if you see here in the box there's a little bit

3:03

of small focal uptake,

3:05

but look at the burden of liver disease on the FDG pet.

3:09

And this was prostate cancer.

3:10

So this patient had bone metastases

3:12

and liver metastases from primary prostate cancer

3:15

and so same initial pathology,

3:17

but now with the disease progression,

3:19

things are now behaving differently

3:21

and here are our few axials

3:23

and we've got our gray scale imaging

3:25

'cause it's really great for the sensitivity with PSMA

3:28

and FDG starting with the liver lesion, you can see

3:32

that there is really no uptake

3:34

where there is this intensely FDG AVID lesion in the

3:38

anterior aspect of the liver.

3:40

Whereas if we look at this bone lesion,

3:41

there's minimal FDG uptake.

3:44

So the bone lesions are have more PSMA expression

3:47

that is retained whereas the um,

3:49

FDG AVID lesions have d differentiated

3:52

further and they're behaving differently.

3:54

So there may be in this patient a role

3:56

for two different therapy lines

3:58

to manage the two different cell lines, um,

4:00

of their metastatic disease.