**3. Methods for the quantification of ECM elements above mentioned**

The methods explained are based on the experience of the group in the study of the ECM in neuroblastic tumor samples.

#### **3.1. Samples**

The study of tissue microarrays (TMAs) have emerged as a tool for rapid analysis for diagnostic and prognostic studies because several markers can be tested in huge amounts of samples [76– 79]. The main advantage of TMAs consists in the standardization of the methods, given that all samples contained in a single TMA are subject to the same protocols. TMA are mainly used to validate biologic markers with potential diagnostic value, which can be used to develop screening programs or enhance a subclassification of a disease [80]. The steps to follow are summarized in **Figure 1**. Alternatively, whole slides for individual samples can be used.

**Figure 1.** Steps followed to construct a TMA. **A)** Hematoxylin & eosin of a sample with two representative areas select‐ ed and their corresponding location in the paraffin block (already perforated). **B)** Beecher Instrument (Silver Springs, MD) and the different parts composing it (1 and 2: fixed plate and receptor block; 3: small needle to perforate the re‐ ceptor block; 4 and 5: mobile plate with one donor block and its hematoxylin & eosin to be able to locate the represen‐ tative regions selected by the pathologist; 6: big needle to extract cylinders from donor blocks; 7: fingerwheel to move in the X axis; 8: fingerwheel to move in the Y axis. **C)** TMA obtained where each sample is represented by 2 cylinders and 2 control cylinders are placed asymmetrically.
