The purpose of this study is to test, customize, and personalize a mobile app-based intervention program in order to help rare and breast cancer survivors cope with fears of cancer recurrence.

Inclusion Criteria:

Phases 1 & 2:

• Breast cancer survivors
• Hx of early-stage breast cancer (DCIS and Stages I, II and III)as recorded in the medical record at MSK or by self-report or by outside correspondence, including a study checklist signed by a physician for patients outside of MSK.
• ≥ 3 months post completion of breast cancer treatment (may be on hormone therapy, such as tamoxifen) with no history of recurrence or metastasis as confirmed by the medical record at MSK, self- report or by outside correspondence
• Age 18 or older
• Able to read and speak English
• An overall fear index score of ≥ 3.0 on the CARS
• If taking medication for mood, anxiety, depression, thoughts, sensory experiences such as hallucinations, or sleep, stable and consistent enough in dosage and use of that medication so as to not result in a clinically significant change as determined by the study PI/co-PI or confirmed by reports in the medical record at MSK or by self-report or by outside correspondence, including a study checklist signed by a physician for patients outside of MSK
• If in non-CBT psychotherapy, stable for at least 8 weeks
• Access to a computer or willingness to come to MSK to complete intervention sessions 2-8 and the 3-month follow-up assessment, if no personal computer.
• For Part 2 only, did not participate in Part 1

Phase 3, Part 1 and 2:

• Hx of early-stage breast cancer (DCIS and Stages I, II, and III) as recorded in the medical record at MSK or by self-report or by outside correspondence, including a study checklist signed by a physician for patients outside of MSK
• Completion of breast cancer treatment (may be on hormone therapy, such as tamoxifen) with no history of recurrence or metastasis as confirmed by the medical record at MSK, by self-report, or by outside correspondence
• Age 18 or older
• English fluency: self-report by subject identifying English as the preferred language for healthcare, and self-reported degree of fluency as speaking English "Very well."
• Score of >/= 12 on the 8-item Cancer Worry Scale
• Score of >/= 2 SDs below the mean on the euro-QOL-Short Form
• Uses an iOS mobile device (may be an iPad)
• If taking medication for mood, anxiety, depression, thoughts, sensory experiences such as hallucinations, or sleep, stable for at least 8 weeks and consistent enough in dosage and use of that medication so as to not result in a clinically significant change as determined by the study PI/co-PI or confirmed by reports in the medical record at MSK or by self-report or by outside correspondence, including a study checklist signed by a physician for patients outside of MSK.

Phase 3, Part 3:

• Hx of early-stage breast cancer (DCIS and Stages I, II, and III) with no history of metastasis as per EMR, by self-report, or by outside correspondence.
• Completion of breast cancer treatment (may be on hormone therapy, such as tamoxifen, or on maintenance medication) as per the EMR or self-report.
• Age 18 or older as per the EMR or self-report.
• English fluency: Self-report by subject identifying English as the preferred language for healthcare, and self-reported degree of fluency as speaking English "Very well"
• Score ≥ 9 on the 6-item Cancer Worry Scale (CWS: this score was found to be optimal to screen for high FCR across cancer types)
• Score of > 2 SDs below the mean on the Neuro-QOL-Short Form
• Uses an iOS mobile device (may be an iPad) as per self-report.
• If taking medication for mood, anxiety, depression, thoughts, sensory experiences such as hallucinations, or sleep, stable for at least 8 weeks and consistent enough in dosage and use of that medication so as to not result in a clinically significant change as determined by the study PI/co-PI or confirmed by the EMR or by self-report or by outside correspondence including a study checklist signed by a physician for patients outside of MSK
• Must reside in the United States.

Phase 4, Parts 2 and 3:

• Hx of early stage (Stages 0, I, II, and III) rare melanoma subtypes (e.g., acral, uveal) and skin (excluding keratinocyte cancers, e.g., basal and squamous cell), gynecological, long-term adult, pediatric rare liquid cancer (in remission only) or other rare cancer per the EMR, by self-report, or by outside correspondence.
• Age 18 or older, as per the EMR or self-report.
• English fluency: Self-report by subject identifying English as the preferred language for healthcare, and self-reported degree of fluency as speaking English "Very well."
• Score ≥ 9 on the 6-item Cancer Worry Scale (CWS; this score was found to be optimal to screen for high FCR across cancer types)
• Score of >2 SDs below the mean on the Neuro-QOL - Short Form
• Uses an iOS mobile device (may be an iPad) as per self-report.
• If taking medication for mood, anxiety, depression, thoughts, sensory experiences such as hallucinations, or sleep, stable for at least 8 weeks and consistent enough in dosage and use of that medication so as to not result in a clinically significant change as determined by the study PI/co-PI or confirmed by the EMR or by self-report or by outside correspondence, including a study checklist signed by a physician for patients outside of MSK
• Completed active treatment (can be on hormonal therapy or on maintenance medication) as per the EMR or self-report.
• Must reside in the United States.

Exclusion Criteria:

Phases 1 & 2:

• Evidence of or treatment for a second primary of cancer EXCEPT basal or squamous cell carcinoma of the skin as confirmed by the EMR, by self-report, or by outside correspondence
• Significant psychiatric or cognitive disturbance sufficient, to preclude providing informed consent or participating in the interventions (i.e., acute psychiatric symptoms which require individual treatment) as determined by the study PI/co-PI or confirmed by the EMR or by self-report or by outside correspondence
• Current participation in cognitive-behavioral therapy (CBT), as confirmed by either self-report* or the EMR, also targets cognitive biases.

Phase 3:

• Evidence of or treatment for a second primary cancer EXCEPT basal or squamous cell carcinoma of the skin as confirmed by the medical record at MSK, by self-report, or by outside correspondence
• Metastatic disease
• Score of \

Rare and Breast cancer survivors will be recruited to the study. There are no physical recruitment sites outside of MSKCC. Participants may be patients who were treated at MSKCC or rare or breast cancer survivors who were treated elsewhere and learned about the study through an advertisement. The study summary and research team contact information will be available/advertised in the community through MSKCC Connections, MSKCC Survivorship Program and the American Cancer Society website.