High‐grade intraductal carcinoma of the parotid gland harboring CTNNA1::ALK rearrangement: Changes in genetic status using genetic testing during treatment with an ALK inhibitor

Abstract Background Salivary gland carcinomas harboring anaplastic lymphoma kinase ( ALK ) rearrangements are rare. Here, we present the pathological characteristics, clinical course, and changes in the genetic status of a salivary gland carcinoma harboring a catenin alpha 1 ( CTNNA1 ):: ALK rearrangement during treatment with an ALK tyrosine kinase inhibitor (TKI). Methods A 59‐year‐old man with a parotid tumor and cervical lymph node metastases underwent total parotidectomy and radical neck dissection. One month after completion of postoperative radiotherapy, the patient experienced multiple recurrences. Results Subsequent treatment with the ALK‐TKI alectinib was initially effective against the intraductal carcinoma harboring CTNNA1 :: ALK rearrangement and TP53 mutation. However, 10 months later the patients' condition deteriorated, and an additional phosphatidylinositol‐4,5‐bisphosphate 3‐kinase catalytic subunit alpha ( PIK3CA ) mutation was detected. The patient ultimately succumbed to multiple organ failure. Conclusion The clinical course suggested the concurrent emergence of TP53 and PIK3CA mutations and ALK‐TKI drug‐selective growth of non‐ ALK rearrangement gene tumor cells.