Introduction
In 1959, the pathologist Virginia Kneeland Frantz firstly described a solid pseudopapillary neoplasm (SPN) of the pancreas in a 2-year-old male patient [
1]. It is a low-grade malignant tumour lacking a specific line of pancreatic epithelial differentiation [
2], accounting for 1–3% of all pancreatic tumours [
3]. Solid pseudopapillary neoplasm is known for its strong female preponderance (F:M = 10:1); in fact, it affects women less than 30 years old in 85% of cases [
4], while men are rarely affected. About 20–25% of SPNs occur in patients younger than 18 years [
4].
The clinical presentation is usually non-specific. The most frequent symptoms are abdominal pain or discomfort, a palpable mass, and compression of the stomach, duodenum, or main biliary duct related to the large size of the tumour [
5]. Some patients are completely asymptomatic, and the SPN may be detected incidentally by imaging studies, or by routine physical examination. Laboratory tests are normal, hormonal activity is absent and tumour markers are generally unremarkable [
5].
A complete surgical excision is curative in patients with a SPN limited to the pancreas. Up to 10–15% of SPNs show malignant behaviour and distant metastases, usually to the liver and peritoneum [
6]. Nevertheless, SPN is generally associated with an excellent long-term prognosis, with a reported 10-year disease-specific survival rate of 96% [
7], even when including the resection of distant metastases [
8]. Currently, no specific chemotherapy regimens are available.
In recent years, the reported number of SPNs in the English literature has increased sevenfold since 2000 [
9]. The knowledge of this rare pancreatic tumour has become better than before, and the quality and use of cross-sectional imaging has improved [
9]. The interest in this disease is increasing, especially in those rare SPNs that develop in male patients. In this specific field, the available literature is limited. We report three new cases of pancreatic SPN in male patients, and we performed a review of the English literature of pancreatic SPN in males from 1980, evaluating their clinic-pathological features, surgical treatment and outcome.
Discussion
Solid pseudopapillary neoplasm (SPN) of the pancreas is a rare neoplasm. It mainly affects young women, suggesting a role form hormonal factors, but no association with endocrine diseases has been reported so far [
2]. Its natural history is still uncertain, especially in those rare SPNs that develop in male patients. This neoplasm may derive from genital ridge-related cells [
13], or pluripotent stem cells of the genital ridges [
14] that become attached to the primordial pancreas during embryogenesis. Moreover, extra-pancreatic SPNs have been reported in retropancreatic tissue, ovary, and testis [
2]. A systematic review on SPNs by Law et al. [
9] reported of 336 SPNs in men collected up to 2012 (12% of the whole cases), as from the experience of our institution, with 15.8% of males among all patients operated for a SPN in the last 30 years. The present systematic review comprised 1052 total SPNs, with a SPN rate in males of 23.4%, resulting higher than previously reported. However, this finding is due to the article selection process, which provided for the exclusion of series including female patients only.
In male patients, SPNs show an older age at presentation when compared with that in female patients [
6,
15,
16]. In the present review, the oldest patient was 78 years old, and adult patients represented 73.8% of total SPNs in males (mean age, 42.2 years). The late occurrence of SPN in males might be the result of a long-term exposure of the ectopic ovarian like stroma to normal level of female sex hormones [
16], since normal levels of both progesterone and estrogen were detected in male patients [
16]. When comparing young (less than 18 years old) and adult male patients with SPNs, the former showed a slightly larger mean tumour size than the latter (7.0 cm vs. 5.7 cm), as Bender et al. reported of a mean SPN size of 8.2 cm in young patients [
17]. Regarding tumour site, adult male patients showed a SPN located in the body–tail region of the pancreas in the majority (65.8%) of cases, whereas in young males, SPNs may be located in the pancreatic head and body–tail in 41.4% and 56.9% of cases, respectively. This finding may suggest that distal pancreatic lesions, which are less likely symptomatic, may be detected only later in life, irrespective of their time of onset.
The clinical presentation of SPN usually consists of non-specific symptoms (i.e. abdominal pain or abdominal discomfort), and patients may be even asymptomatic. The number of incidentally detected SPNs has grown, accounting for about 40% of all SPN cases (irrespective of gender) [
9], and in our systematic review 35.9% of patients were asymptomatic at diagnosis. No tumour markers or routine laboratory parameters have been identified for the diagnosis of SPNs, thus pre-operative diagnosis is based on imaging studies and cytopathological examination of FNA samples. Pre-operative diagnosis of SPNs may be challenging, especially in male patients for whom this type of exocrine neoplasm is less often suspected. In these patients, the main alternative diagnosis may be a pancreatic NEN. The introduction of CT scan in the 1980s has increased the pre-operative diagnostic accuracy for SPNs. Ultrasound, CT scan and MRI typically show a large well-circumscribed, heterogeneous mass with varying solid and cystic components [
18], demarcated by peripheral contrast enhancement corresponding to a fibrous pseudocapsule, and occasional calcifications. Recently, Wang et al. [
19] reported that calcifications and enhanced solid components within the unenhanced cystic components (defined “floating cloud” sign) are useful features in discriminating SPNs from hypodense pancreatic NENs at CT scan [
19].
In our systematic review, most of the patients underwent a CT scan, but an
18F-FDG PET-CT (or PET-MRI) was performed in only 12 (5.5%) patients. Although the intensity of
18F-FDG uptake in SPNs may vary widely due to tumour heterogeneity [
20], in a previous study [
21] we showed that only two (3%) out of 69 SPNs collected in the literature were PET negative. Some authors compared the CT [
22‐
24] and MRI [
25] imaging features of pancreatic SPNs between male and female patients. Males were significantly older than female patients, and irrespective of tumour size, SPN in males had mainly a solid component, whereas female patients had a significantly high rate of cystic lesions. The high metabolism of SPNs at FDG-PET seems to have a direct relationship with tumour cellularity [
26] and with the solid (cellular) component of SPNs [
26], irrespective to malignant behaviour. Thus, SPNs with a predominant solid component, as those detected in males, can be easily identified based on a marked avidity for
18F-FDG (SUVmax range 3.5–18.3) [
27], and differentiated from pancreatic NENs, which usually have a poor
18F-FDG uptake and a low SUVmax value [
27]. In the present review, SPNs showed an intense tracer uptake at FDG-PET in 80% of cases (mean SUVmax 5.0). In the presence of a pancreatic mass suspected for a SPN or a NEN, even in case of liver metastases, surgery would be the treatment of choice. However, a correct diagnosis may be crucial in patients not fit for surgery, giving them the chance of a correct alternative treatment (i.e. somatostatin analogues for NENs).
Some authors [
28] stated that radiologic diagnosis is sufficient for SPNs, especially when planning surgery. However, obtaining a pre-operative histologic diagnosis may be sometimes advisable, and EUS-guided FNA is the most frequently used procedure and a valuable technique for its diagnostic accuracy [
29‐
31]. In the present review, when considered together imaging studies and FNA allowed a correct pre-operative diagnosis in 53.6% of cases. Notably, only 40 (19.1%) patients underwent a pre-operative FNA, which resulted positive for SPN in 82.5% of cases. Since a low amount of material may be available through FNA and immunohistochemistry is mandatory for diagnosis, the correct diagnostic antibody panel should be accurately chosen [
32]. In young patients, FNA may not differentiate between SPN and pancreatoblastoma [
33], whereas in adults a misdiagnosis with a pancreatic NEN may be avoided detecting the highly specific patterns of E-cadherin and β-catenin staining [
34].
Histologically, SPNs are characterised by solid areas alternated with a pseudopapillary pattern and cystic spaces. These features result from degenerative changes occurring in the solid neoplasm [
35], without increased mitoses or cytological atypia [
36,
37]. These neoplasms always show expression of β-catenin, thus positive nuclear and cytoplasmic staining for β-catenin are now considered essential diagnostic criteria [
2]. Immunoreactivity for cytokeratins, synaptophysin, and CD56 can be observed in 30% to 70% of cases, whereas chromogranin is usually negative [
2]. The tumour cells also express vimentin, CD10, CD99, CD56, alpha1-antitrypsin, and progesterone receptors [
2]. In the present review, β-catenin was always positive when performed, whereas progesterone receptors were detected in 77.8% of cases. Tien et al. [
38] found no difference in immunostaining for sex hormone-receptor proteins, or in pathological features when stratified for gender.
In the present review, 206 (97.2%) patients underwent surgery, which consisted in standard pancreatic resections in 90.4% of cases. Tumour enucleation and incomplete excision should be avoided, due to the risk of tumour dissemination and a high recurrence rate [
18]. Some authors proposed extended and more radical surgery in men with SPNs, due to the high likelihood of aggressive disease [
15], but no significant differences in terms of follow-up outcomes have been demonstrated between male and female patients [
39]. Surgery continues to be considered the standard of care for localised SPNs, and it is accepted for metastatic disease [
40]. In the present review, among 10 patients who presented with distant (mostly liver) metastases, four patients underwent surgery of the primary SPN, and two of them were still alive with disease 29 and 70 months after surgery, respectively.
No established chemotherapy regimen is currently recommended for SPNs, but in case of metastatic disease, combined systemic and loco-regional treatments may be used with a palliative intent. Among 10 patients presenting with distant metastases, seven received a combined treatment (i.e. resective or palliative surgery, chemotherapy, and/or TAE), and three of them died of disease after a mean follow-up of 12 months. Concerning 14 patients with disease recurrence (mean DFS 43.1 months), six received a combined treatment (i.e. chemotherapy, TAE, radiotherapy, and/or re-do surgery), and five of them were alive with disease up to 180 months after surgery. Aggressive SPNs (defined as SPNs that locally invaded, recurred, or metastasised) showed a 5- and 10-year survival rate of 71.1% and 65.5%, respectively [
41].
To date, a standardised follow-up protocol is not available, but a long follow-up should be performed as SPN recurrence may occur even 10 years after resection [
42]. In our review, 14 (7.2%) patients showed a disease recurrence (i.e. liver, or peritoneum), after a mean DFS of 43.1 months (up to 96 months) after surgery. The vast majority (89.5%) of patients were alive with no evidence of disease after a mean follow-up of 47 (range 4–180) months. This finding confirms that SPNs may have an excellent prognosis after radical surgery [
18].
Limitations of this systematic review include the variation in the extent and quality of variables collected. Moreover, many institutional series presenting aggregate data of female and male patients had to be excluded from the present review.
In conclusion, pancreatic SPN in males occur mainly (73.8%) in adult patients rather than in childhood. In case of detection of a solid-cystic pancreatic mass, a diagnosis of SPN should be taken in account even in asymptomatic males with a large tumour size. Cytopathologic examination may help the therapeutic planning, particularly in case of metastatic or non-resectable disease. A high hypermetabolism at 18F-FDG PET (CT or MRI) strongly suggests a SPN in the differential diagnosis with a pancreatic NEN. Surgery is the treatment of choice in pancreatic SPN, and a long disease-free survival up to 180 months may be achieved after radical resection. In metastatic setting, a multimodal treatment may provide a long-term survival up to 70 months.
Publisher's Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.