How can I deal with that? I did not see any query to interrogate sample information. In addition, I cannot wget the web page and look into the source code because of the "?acc=GSM1442240" part in the URL. Finally, I did not find a clinical spreadsheet available on GEO or provided by the authors in their paper.
I answer my own question since I found a convenient way to do that.
There are two problems with the GEOquery package from BioConductor. First: GEOquery required downloading the whole data again (unless I missed an option to only get sample information?) and the raw dataset is nearly 100 Gb. Knowing that I already downloaded the complete dataset, processed it and deleted it due to its volume. Second: I understood that SOFT formatted file contain sample information but GEOquery took ages to load a ~36Gb file (I had to download that one too). I guess that if the dataset was smaller, GEOquery could have been a convenient tool to do that. However, it seems a non-viable option in my case.
What I did: a basic UNIX grep command on the SOFT formatted file. At some point (after the micro-array format definition), sample information are indicated. I caught the pattern to got what I wanted:
Basically, this command captures two lines per sample: sample name (starts with ^SAMPLE) and sample ethnicity (starts with !Sample_characteristics_ch1). paste is used to merge two consecutive lines into a single one. sed removes patterns. Output (tab delimited):