What is Neuroblastoma?

There are many websites, which explains what neuroblastoma is, but reading through all of them might be very confusing. Even the doctors who treat Saskia, say that this type of cancer can be a confusing cancer. Therefore Saskia will have to go through many test in order to determine the method of treatment.
The following description is from one of the largest online medical libraries, modified to suit our understanding from how it applies to Saskia:

Neuroblastoma is a malignant (cancerous) tumour which develops from nerve tissue. It occurs in infants and children and can occur in many areas of the body. Most neuroblastomas begin in the abdomen in the adrenal gland or next to the spinal cord, or in the chest. They may also start in other areas. In Saskia's case it started in the neck. Neuroblastomas can spread to the bones (face, skull, pelvis, shoulders, arms, and legs), bone marrow, liver, lymph nodes, skin, and around the eyes (orbits). In most patients, the neuroblastoma has already spread when it is first diagnosed.
The first visual sign of Saskia's tumour was back in May 2011. After an ultrasound, the prognosis was that it would disappear by itself. And although it did reduce in size, it never really disappeared. Late October 2011, the lump had grown and Saskia felt more uncomfortable. A specialist advised a chest X-ray which was done on 8 November, followed with a biopsy on 11 November. On 14 November it was clear that the lump would not disappear by itself and that it was neuroblastoma.