Oncology and psychiatry intersect

Ms. Patmore is a 51-year-old premenopausal female who presents to her family physician’s office with an ongoing episode of severe depression. She is accompanied by her daughter, who reports her mother’s inability to sleep, a lack of appetite, low energy and speech latency.1 Past medical history is significant for major depressive disorder (MDD) diagnosed five years ago and managed effectively in the past three years with the selective serotonin reuptake inhibitor (SSRI) fluoxetine (20 mg/d). Ms. Patmore’s daughter reports their family’s recent concerns that Ms. Patmore is becoming increasingly depressed, with similar characteristics as her initial depressive episodes five years previously. Ms. Patmore has a recent (1 year) history of estrogen-receptor positive invasive ductal carcinoma (IDC; T1N1 disease) that was identified on routine mammogram. She underwent a unilateral mastectomy 10 months ago and surgical reconstruction is pending. Post-operatively, Ms. Patmore began adjuvant therapy with oral tamoxifen (20 mg/d) as her cancer was found to be estrogen receptor (ER) positive.2 Her daughter reports that at that time, fluoxetine was replaced with the SSRI escitalopram (20 mg/d), owing to the propensity for drug interactions between certain SSRIs (including fluoxetine) and the cytochrome P450 (CYP) 2D6 enzyme, which metabolizes tamoxifen to its active metabolite, endoxifen.3 Over the past three months, Ms. Patmore’s depressive symptoms have returned and worsened.