**Core Concept**
Conventional cytogenetics in solid tumors, particularly in carcinoma of the cervix (Ca Cx), can be challenging due to the difficulty in obtaining and analyzing tumor cells. This is because solid tumors often consist of a mixture of cancer and normal cells, making it hard to isolate and study the cancer cells specifically.

**Why the Correct Answer is Right**
The correct answer is related to the fact that solid tumors, including Ca Cx, often have a high degree of cellular heterogeneity, making it difficult to obtain a representative sample for cytogenetic analysis. Additionally, the presence of normal cells can contaminate the sample, leading to inaccurate results. In contrast, hematological malignancies, such as leukemia, typically have a higher proportion of cancer cells and are often easier to analyze using conventional cytogenetics.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because while it is true that solid tumors can be heterogeneous, this is not the primary reason why conventional cytogenetics is difficult in Ca Cx.
**Option B:** This option is incorrect because while the presence of normal cells can contaminate the sample, it is not the primary reason why conventional cytogenetics is difficult in Ca Cx.
**Option C:** This option is incorrect because while the use of interphase fluorescence in situ hybridization (FISH) can be challenging in solid tumors, it is not the primary reason why conventional cytogenetics is difficult in Ca Cx.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that solid tumors often require specialized techniques, such as FISH or molecular cytogenetics, to accurately analyze their genetic abnormalities.

**Correct Answer: D. Tumor heterogeneity.**