docs: def get_fresh_primary_tumors(biospecimen):
      """Filter biospecimen data to only keep non-FFPE primary tumor samples.
      
      Parameters
      ----------
      biospecimen : `pandas.DataFrame`
          The biospecimen data frame. This type of data frame is returned by
          :meth:`get_biospecimen_data`.
      
      Returns
      -------
      `pandas.DataFrame`
          The filtered data frame.
      """
      df = biospecimen  # use shorter variable name
  
      # get rid of FFPE samples
      num_before = len(df.index)
      df = df.loc[~df['is_ffpe']]
      logger.info('Excluded %d files associated with FFPE samples '
                  '(out of %d files in total).',
                  num_before - len(df.index), num_before)
  
      # only keep primary tumors
      num_before = len(df.index)
      df = df.loc[df['sample_type'] == 'Primary Tumor']
      logger.info('Excluded %d files not corresponding to primary tumor '
                  'samples (out of %d files in total).',
                  num_before - len(df.index), num_before)
  
      return df