We claim:
1. A method for treating a subject having a p53 dependent tumor cell comprising:
(a) determining the level of NBS- 1 protein expressed in that tumor cell and in a corresponding non-malignant cell;
(b) selecting subjects having a NBS- 1 protein level comparable or below that in a corresponding normal cell; and

(c) elevating the level of NBS- 1 in said tumor cell, whereby said NBS- 1 interacts with p53 responsive promoters.

2. The method of claim 1, wherein the level of NBS- 1 is determined by use of an antibody to NBS- 1.

3. The method of claim 1, wherein the NBS-1 protein level is also compared to the level of p53 expression in said tumor cell, and subjects are selected having tumor cells where the NBS-1 protein level is less than 10% that of p53.

4. The method of claim 1, wherein the level of NBS-1 is enhanced by transfecting the tumor cell with a vector containing a gene encoding NBS- 1 or a functional fragment thereof, wherein said functional fragment is a fragment that interacts with a p53 responsive element in a p53 responsive promoter.

5. An antibody that specifically binds to NBS-1.

6. An antibody raised to the carboxy portion of NBS- 1.

7. The antibody of claim 5 or 6, which is selected from the group consisting of polyclonal antibodies, monoclonal antibodies and single chain antibodies.

8. The antibody of claim 7, which is a monoclonal antibody.

9. A kit containing a probe for NBS-1 protein levels with instructions for measuring said levels in a malignant cell.

10. The kit of claim 9, wherein the probe is an antibody that specifically binds to NBS- 1.