Neuroblastoma is an embryonic malignant tumor that affects the normal development of the sympathetic nervous system. It represents the third leading cause of cancer in children under 15 years of age (after high-risk leukemias and central nervous system tumors) and is responsible for 15% of cancer deaths [1][2].

Its high incidence in developed countries (7% - 10%) is due to the over-exploration of cancers detected by non-invasive imaging and screening tests [3]. In contrast, in African and Asian populations, the incidence rates are lower. This may be explained by a higher prevalence of other childhood cancers within these populations [4][5].

A morphological study is often sufficient, as neuroblastoma is the typical example of a “small round blue cell” tumor, interspersed with a neurofibrillary matrix. However, the use of a panel of immunohistochemical markers is recommended in some cases.

Neuroblastoma is a very complex and heterogeneous disease. This heterogeneity is associated with numerous factors such as age at diagnosis, stage of the disease, biological and histological characteristics of the tumor, and numerous genetic alterations such as MYC-N amplification and ploidy [6]. All these factors influence the prognosis and treatment options.

The objective of this work was to determine the epidemiological profile, and to describe the histopathological, immunohistochemical, and prognostic aspects of neuroblastoma in the Anatomy and Pathological Cytology (APC) laboratories of Dakar.

We conducted a cross-sectional, retrospective, multicenter study in two (2) Anatomy and Pathological Cytology (APC) laboratories in the Dakar region (Senegal): Hôpital Général Idrissa POUYE (HOGIP) and Cheikh Anta Diop University (UCAD). This study was based on archived neuroblastoma pathology reports from these two (2) APC laboratories.

Epidemiological data: Frequency, age, sex were reported,

Anatomopathological data:

Inclusion Criteria:

All histopathological examination reports concluding neuroblastoma and confirmed by immunohistochemical analysis were included.

Exclusion Criteria:

All histopathological examination reports for which the blocks were not found or for which immunohistochemical analysis did not confirm neuroblastoma were excluded.

Anatomopathological data such as lesion location, topography, macroscopic and microscopic features, immunohistochemical profile, and histoprognostic stage, obtained for each patient, were archived in a computerized database using Excel software. A descriptive analysis was performed for each variable.

The processing of samples follows the standard procedures in anatomical pathology. Upon receipt, a registration number is assigned and recorded in the department’s log. Simultaneously, the following are verified:

- The correct completion of the anatomical pathology examination request form,

- The type of organ sampled,

- The date of sampling,

- And the presence or absence of a fixative (formalin).

We retrieved from the archive’s paraffin blocks of selected samples (for immunohistochemical analysis) and slides (stained with H&E) of all samples selected for our study (for review).

Immunohistochimy:

Immunohistochemical confirmation was performed in Morocco for samples from the first five years (2017-2021) and in Dakar for 2022 and 2023. All slides stained with H&E (Hematoxylin-Eosin) and confirmed by immunohistochemistry were reviewed.

Neuroblastomas characteristically show positive staining for synaptophysin, chromogranin, and CD56.

S-100 protein staining was used to identify cytodifferentiated cells such as Schwann cells.

However, they do not show immunoreactivity for EMA, cytokeratin, vimentin, or CD45.

The following antibodies were tested: CD45, CD56, Synaptophisin, Ki67.

Epidemiological and Clinical Data:

During the study period, 35 cases of neuroblastoma were identified, representing 5.27% of all pediatric tumors (n = 664). The distribution of cases per year is shown in Table 1(A).

The mean age of the patients was 5.42 years [3 months-17 years] (Table 1(B)), with a male-to-female sex ratio of 0.94 (Table 1(C)). The majority of patients (51.42%) were diagnosed before the age of 5.

Table 1. Epidemiological characteristics of patients.

Localization:

In our series, 33 patients (94.29%) presented with a single primary neuroblastoma, while 2 patients (5.71%) presented with a dual primary lesion at two different sites. The localization was not specified for one patient (2.86%), and 9 patients (25.71%) had metastatic disease at diagnosis (Table 2).

Table 2. Distribution of neuroblastoma according to topography.

Anatomopathological Data:

We received 19 biopsy samples (54.28%) and 16 surgical specimens (45.71%). The most frequently observed macroscopic appearance was that of a firm tumor with a multinodular surface, with tissue sections exhibiting necrotic and hemorrhagic changes (Figure 1).

Figure 1. Macroscopic examination: White-gray multinodular tumor displacing the kidney. ACP HOGIP/UCAD Laboratory, Dakar.

A histopathological appearance of differentiated neuroblastoma (small, round, sometimes elongated cells with finely dispersed chromatin in a “salt and pepper” pattern and a small amount of cytoplasm with indistinct cytoplasmic borders) was found in 30 cases (85.71%). A small round cell tumor was suspected in the remaining 5 cases (14.29%) (Figures 2-4).

Immunohistochemical analysis was performed on all patients in the series. The neuroblastomas characteristically showed positive staining for synaptophysin, chromogranin, CD56, and neuronal-specific enolase. S-100 protein staining was used to identify cytodifferentiated cells such as Schwann cells (Figures 5-8).

Figure 2. Microscopy: Lymph node infiltrated by a neuroblastoma, Hematoxylin and eosin stain ×100. ACP HOGIP/UCAD Lab. Dakar.

Figure 3. Neuroblasts grouped in discose masses and trabeculae with loose fibrillar foci of neuropil. Hematoxylin and eosin ×100. ACP HOGIP/UCAD Lab. Dakar.

Figure 4. Small, round, sometimes elongated cells with finely dispersed chromatin in a “salt and pepper” pattern and a small amount of cytoplasm with indistinct cytoplasmic borders. (HE ×40) ACP Lab HOGIP/UCADDakar.

Figure 5. CD45 positive in residual lymphoid tissue. ACP HOGIP/UCAD Lab. Dakar.

Figure 6. Positive diffuse synaptophysin. ACP HOGIP Lab/UCAD, Dakar.

Figure 7. Diffuse and homogeneous membrane labeling with CD56 (×40). ACP Lab HOGIP/UCAD. Dakar.

Figure 8. KI67 60% nuclear labeling. ACP HOGIP/UCAD Lab, Dakar.

Histopathological and Prognostic data:

An age > 1 year and abdominal location are associated with a poor prognosis. In our study, among the 35 neuroblastoma cases, 33 were older than one year, representing 92.85% of cases. Abdominal location was described in 8 patients, representing 22.86% of cases. Cervical and pelvic locations were associated with a good prognosis and represented 8.57% and 11.43%, respectively.

According to the INSS (International Neuroblastoma Staging System) classification, 74.29% of patients were at Stage 2B and 25.71% at Stage 4. According to the INPC (International Classification of Neuroblastoma Pathologies - Shimada System) classification, 30 patients had unfavorable histology, representing 85.71%, and 5 had favorable histology, representing 14.29% (Table 3).

Table 3. Distribution of patients according to primary sites, INSS classification and Shimada histological classification.

Neuroblastoma (NB) is an embryonic cancer arising from neural crest stem cells. This cancer is the most common malignancy in infants and the most common extracranial solid tumor in children [7][8].

The incidence of neuroblastoma in Senegalese children is low compared to that reported in developed countries. In Senegal, neuroblastoma ranks fifth after nephroblastoma, retinoblastoma, lymphoma, and sarcomas. It represents nearly 4% of the activity of the Pediatric Hematology-Oncology Unit in Dakar [9]. In our study, this incidence was 5.27 cases per 1,000,000 children per year. A previous study conducted by the Franco-African Pediatric Oncology Group obtained an incidence of 4 cases per 1,000,000 children per year [10]. The incidence reported here is similar to that of several Asian, African, and Latin-American countries.

It is likely that the incidence of neuroblastoma in developing countries is actually lower than that reported in developed countries. However, this variation should be interpreted with caution, as data from developing countries are primarily hospital-based and rely on time-limited surveys, which do not allow for valid epidemiological conclusions [10]-[12].

Limited information beyond single-institution experiences regarding neuroblastoma outcomes in Low and Middle Income Countries (LMIC) are available [13]. LMICs often lack functioning cancer registries, and existing ones fail to collect comprehensive data on paediatric cancers [14].

Despite the progressive though slow advances in neuro-oncology care, research, and diagnostics in sub-Saharan Africa (SSA), the epidemiological landscape of pediatric brain tumors (PBTs) remains underestimated [15].

The valuation of neuroblastoma research heterogeneity at African country level is unspecified [16].

Senegal does not have screening programs, such as those used in several developed countries, which have demonstrated that patients can experience spontaneous regression in more than 50% of cases [17][18].

In our study, the mean age of patients at diagnosis was 5.42 years. It was 24 months in the United States, 19 months in the United Kingdom, 32 months in Morocco, 27 months in Mexico and Denmark, 30 months in Egypt, 36 months in Algeria, and 43 months in Türkiye [10][12][19]-[21]. The majority of patients are between 1 and 5 years old at diagnosis. This can be attributed to the spontaneous regression of neuroblastoma in the younger age group (<1 year), the lack of diagnosis in primary healthcare centers, and the nonspecificity of symptoms, which can lead to delayed diagnosis.

Several studies have reported a male predominance of neuroblastoma (sex ratio ranging from 1.1 to 1.5) [3], while in Morocco, a marginal female predominance has been identified (sex ratio: 0.8) [22]. In our study, we noted a female predominance with a sex ratio of 0.94.

Only histology confirms the diagnosis of neuroblastoma, and it is often performed after surgical examination. The histopathological examination revealed in all our patients a diffuse proliferation of small, round, sometimes elongated cells with salt-and-pepper chromatin, little cytoplasm, and indistinct cytoplasmic borders.

The classification of infantile NB proposed by Shimada and colleagues incorporates several aspects, as well as the proportion of differentiating elements (i.e., ganglion cells), the mitosis-karyorrhexis index (MKI), defined as the number of cells undergoing mitosis and karyorrhexis (the denominator is 5,000 neuroblastic cells), and the patient’s age. Patient age, in itself, is a powerful prognostic factor in children with NB. Tumors are classified as histologically favorable or unfavorable based on stromal content (rich or poor Schwannian stroma), degree of neuroblastic differentiation, MKI, and age at diagnosis. The entry point into this classification system is the assessment of the stromal “character”. The International Classification of Neuroblastoma Pathologies (INPC) has been used to predict prognosis. This classification is similar to that of Shimada and colleagues, being age-related and based on differentiation, the presence or absence of Schwannian stroma, and MKI.

The International Neuroblastoma Staging System (INSS) classification subdivides neuroblastoma into five stages numbered 1 to 4, in addition to stage 4S. The detection of distant metastases is a major criterion in the classification of neuroblastoma. Indeed, as soon as a distant metastasis is discovered, the tumor is classified as stage 4, except for metastases confined to the skin, liver, and bone marrow before the age of 1 year, which are classified as 4S “special”.

Regarding the diagnostic stage and Shimada histological differentiation, as in the literature, we found no association between favorable histology and localized stages (I and II), or between unfavorable histological ratio and advanced stages (III and IV) [23][24]. Nevertheless, histological evaluation will be necessary in all cases we study in the future to assess this correlation more precisely.

It has been emphasized that neuroblastoma occurs sporadically and that only 2% or fewer patients have a family history of neuroblastoma; however, there are a large number of cases of distinct cancers in family members of patients with neuroblastoma [25]. In our study, no cases of familial neuroblastoma were observed. Based on these data, we believe there may be a non-specific genetic susceptibility to neuroblastoma.

Neuroblastoma is the most common extracranial solid tumor in children. Its incidence in Senegal remains low, and diagnosis is often delayed. The most frequently observed macroscopic appearance was that of a firm tumor with a multinodular surface. The diagnosis is histological, and in our study, the poorly differentiated subtype was predominant. Immunohistochemistry allowed us to confirm this diagnosis using various specific neuronal markers such as synaptophysin, chromogranin, CD56, and enolase.

Limits: the relatively small sample size, due to the rarity of neuroblastoma and the two-center recruitment, limits statistical power and the possibility of conducting in-depth comparative analyses. The retrospective nature of the study also exposes the patient to information bias, due to clinical and histopathological records that were sometimes incomplete or heterogeneous. Furthermore, limited access to complementary techniques such as cytogenetic or molecular analyses (particularly the evaluation of MYCN amplification and associated chromosomal abnormalities) prevented optimal prognostic stratification according to international standards.

Ethical statement: all procedures were conducted in accordance with the Declaration of Helsinki and adhered to national and institutional ethical guidelines.