Prostate cancer is a malignant neoplasm that occurs in older men [1]. In Mexico, it ranks second in causes of death from cancer, after lung [2].

Risk factors include age, since most of the prostate cancer diagnosis appears in men over 64 years of age, first-degree family history, black African-American race, and a high-fat diet [3].

The diagnosis is determined by the prostate specific antigen (PSA), the Gleason score and the extent of the tumor. Various imaging methods are used for initial staging. Magnetic resonance imaging (MRI) shows promising results in locating the tumor and improves the precision of ultrasound-guided biopsy [4], however, despite the fact that European guidelines recommend the use of magnetic resonance imaging in the event that the tumor does not affect other organs, the images suffer from a certain limitation, especially in the central and transition areas [5] [6].

● Review of the initial experience in the use of PET/CT with ¹⁸F-PSMA.

● Average value of hepatic uptake SUV Lean average (SUVlave).

● Age.

● Analysis of the location of metastases.

● Describe and divide the uptakes of non-prostatic tumors and the focal uptakes in the rib without anatomical representation with ¹⁸F-PSMA.

● Determine the relationship between the level of prostate specific antigen (PSA) and positive uptakes for prostate cancer, by PET/CT with ¹⁸F-PSMA.

● Reason for the study.

● Focal, multifocal or diffuse prostate.

● APE level.

In the age analysis, we observed that the average was 70.2 years, median 70 and a mode of 73 years. The youngest patient was 42 years old and the oldest patient was 93 (Table 2).

Mean age = 70 age. Standard deviation = 57.47.

Prostate cancer is the second malignant tumor and the second most frequent cause of death in men, PET/CT with ¹⁸F-PSMA has proven to be a fundamental non-invasive technique in the initial staging in high-risk patients, important in the planning of the surgical approach, functional in the planning of radiotherapy, location of the tumor in biochemical recurrence, useful as a guide for biopsy in patients with high suspicion of cancer with negative previous biopsy results, and to assess the response to treatment.

The objective of this study is to evaluate the results obtained in the scans carried out with PET/CT with ¹⁸F-PSMA during the period: February 2019 to September 2020.

We measured the SUVlave (SUVLean average) in the liver of each one, the highest value found was 21 and the lowest was 1.1, this last value corresponds to a patient with extensive tumor burden (superscan), we found a mode of 10.5 and an average of 9.7. The liver belongs to the physiological uptake of ¹⁸F-PSMA, when placing this reference ROI in the liver, verify that the gallbladder is not included.

The acquisition time of most studies (mode) was 63 minutes. 183 minutes the longest and the shortest at 54 minutes. Although the acquisition times were variable, the analyzes have an appropriate quality, with no alterations in the white background relationship.

The average age was 70.2 years, with a mode of 73 years, 124 patients are in the range of 62 to 73 years, our youngest patient with 42 years and our oldest patient 93 years. Our result agrees with the referenced literature, where age is recognized as a risk factor, since most of the prostate cancer diagnosis appears in men older than 64 years.

In the positive PET/CT, the most frequent involvement was observed in lesion exclusively in the prostate with 29.7% (82) with a predominance of multifocal lesions; second, involvement of the prostate + lymph nodes + bone lesions with 21.2% (58) studies.

Surgical bed + bone metastases and surgical bed + lymph nodes were the least frequent with 8 and 10 studies respectively.

37 studies (13.4%) presented nodes smaller than 5 mm with radiopharmaceutical uptake.

As unusual findings, we found 7 pulmonary metastases, 3 liver, 3 in the penis, 1 splenic, 1 of axillary lymphadenopathy, 8 cervical on the left side and 1 bilateral, 1 nodular lesion in the mesorectum and 1 study in a muscle implant.

Despite the high incidence of prostate cancer, there are few reports of metastatic involvement of the cervical nodes, the predilection for the left side is due to the fact that tumor cells can lodge in the nodes by retrograde spread, due to the proximity of the duct thoracic with left subclavian vein [22].

Hepatic metastases are considered the third site of extra nodal metastases in prostate cancer, after bone and lung; occur in disease refractory to hormonal treatment and in late stages, PSMA uptake in liver metastases may be due to the diversity of prostate cancer phenotypes, predominantly neuroendocrine transdifferentiation [23]. The spleen and muscle are the least common extra nodal metastasis sites [24].

Most of the reasons for the request were staging with 144 studies.

Of the PET/CT performed we have the PSA value in 179. 18 positive studies with PSA < 1.0, of which the minimum value with positive PET/CT was 0.01 ng/ml.

We documented 89 studies with ¹⁸F-PSMA uptake of non-prostatic origin with a predominance in lesions of benign etiology, being the osteodegenerative changes the ones that occurred more frequently, the highest SUVlmax value was 8.5 and the lowest 2.6. Regarding uptakes of non-prostate malignant origin, we present 9 documented studies that present a second primary tumor. In the literature, the association of these uptakes with endothelial neovasculature is well known, showing that PSMA is not exclusive to prostate tissue, this must be taken with relevance, since they can simulate prostate cancer metastasis.

36 studies presented focal uptakes in rib(s) without anatomical representation. In our initial experience, we considered these uptakes as nonspecific, however there was no significant change in size and SUVlmax at follow-up. There is little literature that mentions the nature of these solitary uptake in ribs, however we identified that most of them are of benign origin; taking into account the low uptake of the radiopharmaceutical, the correlation with any signs of trauma and PSA levels [25].

● The acquisition times were varied, from 54 to 183 minutes, all studies have adequate quality for interpretation without alterations in the white-background relationship.

● The average hepatic SUVlave is 9.7.

● Staging occupied the highest percentage of PET/CT indication.

● We detected both unifocal and multifocal uptakes in the prostate with PET/CT with ¹⁸F-PSMA.

● There are uptakes in both benign and malignant lesions due to its expression in the endothelial cells of the neovasculature, that can cause false positives, it is advisable for the doctor who examines the study to have this knowledge in order to obtain an accurate interpretation. There is little literature on solitary uptakes in ribs without anatomical representation with ⁶⁸Ga-PSMA. To our best knowledge, this is the first study with ¹⁸F-PSMA to evaluate and describe uptakes at the rib level. Our results indicate that these findings are considered benign, when PSA levels and the rest of the study are negative.

● Although there is literature that mentions that liver metastases are not so uncommon (25%, 8%) [24] [26], in the 281 positive studies, 2 patients (3 studies) had hyper-uptake liver metastases (0.71%). Among the findings of one of these two patients, we found PSA of 169 ng/mg, histological report of invasive prostatic adenocarcinoma and extensive tumor burden (superscan), the patient died 7 months after the first PET/CT, for which reason we agree with the literature that mentions a mortality of 6 to 14 months with this type of lesion [26]. Liver metastases are frequently associated with neuroendocrine transdifferentiation, which is why PET/CT with ¹⁸F-FDG is useful in metastatic disease with mutation.

● PET/CT with PSMA has the ability to determine bone metastatic status, there are even hyper-uptake bone metastases that we can detect without anatomical representation. We found 11 studies (3.91%) with hyper-uptake lytic lesions, as well as 12 (4.27%) studies with hyper-uptake bone metastases without anatomical representation. In interesting cases, we have the follow-up of patients in evaluation of response to treatment who show partial response to ¹⁸F-PSMA uptake, but with a considerable increase in the number of osteoblastic lesions. This analysis reveals that there may be a disagreement between the functional (PERSIST) and the anatomical (RESIST) assessment; considering that the molecular precedes the morphological (Figure 6).

● We have 179 studies correlated with PSA. 10.05% (18 studies) were positive with PSA < 1.0, this demonstrates the ability of ¹⁸F-PSMA to detect neoplastic activity with low PSA levels.

● We detected 20 studies (7.2%) with supradiaphragmatic lymphadenopathy, which are not so frequent, however, it should be taken into consideration that they may be present in advanced cases of the disease. Supradiaphragmatic extension occurs by hematogenous spread through the vertebral venous system or Batson’s plexus.

● Conventional studies (MRI, ultrasound and CT) have limitations to detect metastatic nodes smaller than 10 mm in the initial staging of patients with high-risk prostate cancer. ¹⁸F-PSMA PET/CT has the potential to detect ma-

lignant infiltration in nodes smaller than 5 mm, which can be considered normal on anatomical studies

● Considering the previous points, PET/CT with ¹⁸F-PSMA has advantages over bone scintigraphy and computed tomography of the abdomen and pelvis for the staging of prostate cancer.

The authors declare no conflicts of interest regarding the publication of this paper.

Gómez Domínguez, J., Schalch Ponce de León, J.M. and Criales Cortés, J.L. (2021) PET/CT with ¹⁸F-PSMA in Patients with Prostate Cancer, Review of the Initial Experience. Open Journal of Urology, 11, 158-175. https://doi.org/10.4236/oju.2021.114015