The Real-world Treatment Satisfaction by Gefapixiant in RCC

Treatment satisfaction

To evaluate the change in treatment satisfaction with the initiation of gefapixiant and to determine factors related to treatment satisfaction by gefapixant. The investigator will assess overall treatment satisfaction using 5-point Likert scale (1. Very dissatisfied 2. Dissatisfied 3. Neutral 4. Satisfied 5. Very Satisfied) at enrolment and 12 weeks after commencing gefapixant from all participants. The investigator will compare the rate of "Satisfaction" (4. Satisfied 5. Very Satisfied) before and after the initiation of gefapixant using the McNemar analysis. Taste disturbance will also be assessed using the Patient-Reported Outcome version of the Common Terminology Criteria for Adverse Events (PRO-CTCAE) classification with slight modification (Grade 0: No change in taste. Grade 1: Altered taste but no change in diet, Grade 2: Altered taste with change in diet; noxious or unpleasant taste; loss of taste; Grade 3 Cease to gefapixant due to altered taste)

The change in cough-specific quality of life and clinical factors

To evaluate the association between the change in cough-specific quality of life (QoL) using the Leicester Cough Questionnaire (LCQ) and the change in clinical factors with gefapixant. The LCQ questionnaire consists of 19 items with 3 domains. It ranges from 3 to 21, with higher scores indicate better cough-specific QoL.

The changes in the core five tastes

To evaluate the changes in the core five tastes such as sweet, sour, bitter, salty, and umami with the initiation of gefapixiant and to determine what tastes are associated with the change in cough-specific quality of life (QoL). The investigator will evaluate threshold of five basic taste perception with a whole-mouth method using a series of twofold dilutions of the taste solutions including sweet (sucrose), salty (NaCl), sour (tartaric acid), bitter (quinine HCl), and umami (monosodium L-glutamate). These measurements will be conducted before and 12 weeks after the initiation of gefapixant to investigate which taste will be affected by gefapixant. The investigator will prepare for 8 doubling concentrations of these 5 tastes, respectively. Sucrose, citric acid, NaCl, Munosodium glutamate, and quinine HCL will be used to make solutions.

Seeking biomarkers

To seek biomarkers that can predict the change of cough-specific quality of life by gefapixant. Lack of zinc and copper are well-known cause of taste disturbance. Copper/zinc ratio is reported as a good diagnostic marker for taste disorders. Thus, the investigator thinks that they may be associated with the development of taste disturbance by gefapixant. The investigator will measure them because their levels will be helpful when considering the additional zinc therapy for taste disorder in clinical practice. The investigator will also use airway immune cells obtained from sputum samples to measure the expression CD 39 and CD 73 in sputum.