While testing #98 I ran into the following issue while it was trying to load the Mutations table:

django.db.utils.IntegrityError: insert or update on table "mutations" violates foreign key constraint "mutations_sample_id_6a37562c_fk_samples_sample_id"
DETAIL:  Key (sample_id)=(TCGA-04-1348-01) is not present in table "samples".

Checking https://raw.githubusercontent.com/cognoma/cancer-data/master/data/samples.tsv for the string TCGA-04 turned up nothing, so either the samples table is missing data or the mutations table has rows it shouldn't.