The purpose of this registry is to determine if select patients with CNS metastatic disease can be safely observed rather than treated. The investigators hypothesize that there is a subset of patients with small asymptomatic CNS mets that do not require treatment, these patients can simply be observed and will not have CNS progression.

Subjects will be given a consultation with physician investigators in the department of one of the study investigators, who will introduce the study if the subject is potentially eligible.

Information collected at initial assessment:

• Quality of life survey (FACT-Br)
• History and Physical exam (to include KPS, disease status on most recent non-CNS imaging, chemotherapy history, age).
• Measurement of walking pace: patient will walk a pre- measured 6 meters, patient is to be instructed to walk at a normal pace. The time required to travel this distance will be recorded. For patients that are wheelchair bound or otherwise immobile, the pace will be recorded as '0'.
• Neurocognitive testing (Montreal Cognitive Assessment)
• MRI scan with contrast (must be within 6 weeks)

Observation and Follow-up Visits:

• Patients will be seen at 6 weeks and then every 2 months for follow-up (with physical exam) with repeat MRI with contrast at that time
• FACT-Br survey to be filled out at each follow-up
• Neurocognitive status (Montreal Cognitive Assessment)

Treatment for Progression:

• Progression is defined as: Increase in size to > 1 cm (> 2.0 for patients being treated with targeted therapy); Interval growth of 0.4 cm in 6-8 weeks; Development of edema or increase in edema; Development of symptoms from CNS lesion; Patient preference
• Patients that meet criteria for treatment will be treated at discretion of treating physician; options can include whole brain radiation, radiosurgery, surgery.

The study does not provide financial or other compensation to subjects

Inclusion Criteria:

• CNS metastatic disease that meets the following:
• No lesion greater than 0.8 cm for patients not on targeted therapy with CNS penetration
• No lesion greater than 1.5 cm for patients on targeted therapy with CNS penetration.
• No previous treatment for the observed lesion. Patients may have had other lesions that have been treated as long as there is at least one index lesion that has not been treated. For example, patient may have had 3 lesions treated in March 2012 with radiosurgery and on recent scan is found to have a new 0.5 cm lesion, this patient is eligible.
• Less than 5 untreated CNS lesions.
• Able to have MRI scan with contrast
• All CNS lesions are asymptomatic. Patient may have symptoms from previous treatment or cancer outside the CNS but cannot have symptoms attributable to the current CNS metastatic disease. This is left to the discretion of the treating physician and in some instances is not easy as sometimes CNS metastatic disease is incidental finding to un-related symptoms.
• Eligible primaries
• Lung (NSCLC)
• Lung (SCLC) that have had previous Whole brain radiation
• GI
• Head and Neck
• Gyn
• Prostate
• Breast
• Kidney
• Melanoma
• Sarcoma

Exclusion Criteria:

• CNS lesion that does not meet following:
• No lesion greater than 0.8 cm for patients not on targeted therapy with CNS penetration
• No lesion greater than 1.5 cm for patients on targeted therapy with CNS penetration.
• More than 5 CNS lesions (can have had previously treated lesions by either surgery or radiation, but at time of protocol SRS must have 5 or less untreated lesions).
• Symptomatic CNS lesions
• Ineligible primaries
• Lymphoma
• Primary CNS tumors
• SCLC that has not had previous whole brain radiation
• Leptomeningeal disease in CNS
• Patients unable to have an MRI (secondary for example to metal hardware)
• Patients unable to have MRI contrast (secondary for example to poor renal function
• CNS lesion >0.8 cm in any dimension for patients not on targeted therapy with CNS penetration or >1.5 cm for patients on targeted therapy with CNS penetration.
• Note that there is no KPS cut-off for eligibility