Inclusion Criteria:

• 1. Lactating female participants 18 years of age or older treated with YORVIPATH as part of their usual medical care and who have chosen to breastfeed. Note: The participant must have been taking YORVIPATH for a minimum of 14 days prior to sample collection.
• 2. The major source of infant nutrition must be breast milk (Note: Only one supplemental bottle of no more than up to 8 oz of formula per day will be allowed during the 14 days before start of the study).
• 3. Daily dose of YORVIPATH administered within the last 14 days has been stable.
• 4. Participants recruited from other sources must enroll in the Pregnancy Registry before being allowed to participate in the Lactation Study.
• 5. Written consent or eConsent obtained.

Exclusion Criteria:

• 1. Presence of any medical condition that, in the opinion of the investigator, may impair the ability to breastfeed during this study, including but not limited to mastitis and nipple malformation