Q.63 Identify the correct statements:

1. Tumor cells differ from normal cells by changes in the regulation of growth.
2. Proto-oncogenes encode defective proteins.
3. Tumor cells can display tumor-specific antigens/novel antigens.
4. Several cytokines including IFN and TNF help to mediate tumor-cell killing.

Choose the correct answer from the options given below:

1. A, C and D only
2. B, C and D only
3. A, B and C only
4. A, B and D only

   The correct answer is A, C and D only.

   Tumor cells exhibit dysregulated growth due to oncogene activation and tumor suppressor inactivation, express neoantigens recognizable by immune cells, and succumb to cytokine-mediated cytotoxicity, while proto-oncogenes encode normal regulatory proteins.

   Option Analysis

   A, C and D only
   A: Correct—tumor hallmark is growth deregulation via oncogene activation/tumor suppressor loss. C: Correct—tumor-specific antigens (neoantigens from mutations) or novel antigens trigger immune recognition. D: Correct—IFN-α/β, TNF-α induce apoptosis/Fas upregulation in tumor cells. B false. Correct.

   B, C and D only
   B incorrect: Proto-oncogenes encode normal functional proteins (growth factors, receptors, cyclins); oncogenes are mutated hyperactive versions. A true. Incorrect.

   A, B and C only
   B false (as above); D true—cytokines central to tumor immunosurveillance. Incorrect.​

   A, B and D only
   B false; C true—tumor immunogenicity from mutated proteins displayed on MHC. Incorrect.​

   Tumor cells differ from normal cells primarily through six acquired capabilities (Hanahan-Weinberg hallmarks), with growth dysregulation universal across malignancies.

   Growth Regulation Defects

   Normal cells require mitogenic signals, exhibit contact inhibition, and undergo apoptosis; tumor cells ignore these via RAS/MAPK pathway constitutive activation, p53/RB loss, enabling limitless replication.

   Immunogenicity and Cytokine Response

   Tumor cells display tumor-specific antigens (neoantigens from nonsynonymous mutations) or cancer-testis antigens on MHC-I, targeted by CD8+ T cells/NK cells. Type I IFNs (IFN-α/β) upregulate MHC-I, activate JAK-STAT apoptosis; TNF-α triggers caspase-8 extrinsic pathway in sensitive tumors.​

   Proto-Oncogene Clarification

   Proto-oncogenes (c-MYC, c-FOS, c-SRC) encode physiologic growth promoters requiring one hit for dominant oncogene activation; tumor suppressors need biallelic inactivation. Mutated proto-oncogenes become oncogenes encoding defective gain-of-function proteins.​