Furthermore, they used a quantitative mass spectrometry (MS) method called parallel reaction monitoring (PRM) to confirm that four phosphoproteins—tight junction protein 2 (TJP2), nuclear transcription factor (NFX1), Ral GTPase-activating protein subunit alpha-2 (RALGAPA2), and cGMP-dependent protein kinase 1 (PKG1)—were significantly upregulated in patients with breast cancer [42]. Here, PRKG1 is linked to breast cancer.