**Core Concept:** Primary amenorrhea refers to the absence of menarche (first menstrual period) in a girl who is more than 15 years old. A 19-year-old patient presenting with primary amenorrhea and having XY chromosomes raises suspicion of a sex cord-stromal tumor in the ovary.

**Why the Correct Answer is Right:** In this case, the correct answer (C) is related to sex cord-stromal tumors. These tumors are benign neoplasms that can develop within the gonads (ovaries in females) and are characterized by the overproduction of sex hormones. In this patient, the XY chromosomal pattern indicates that the tumor is likely to be a sex cord-stromal tumor. These tumors are more common in females with XY chromosomes, as they produce androgens (male sex hormones) instead of estrogens (female sex hormones).

**Why Each Wrong Option is Incorrect:**

A. Female sex characteristics (breast development) and the absence of body hair suggest that the patient has normal female sex characteristics. This option is incorrect as the patient has XY chromosomes and develops androgens from the sex cord-stromal tumor, not estrogens.

B. This option is incorrect as it refers to a genetic disorder, which is not supported by the patient's clinical presentation and XY chromosomes.

D. This option is incorrect as it relates to Turner's syndrome, which would result in a 45,XX karyotype (two X chromosomes) and not XY chromosomes.

**Clinical Pearl:** Sex cord-stromal tumors are relatively rare, accounting for approximately 1% of all ovarian tumors. They can present with various symptoms depending on the hormonal profile produced. In this case, the patient with XY chromosomes has developed androgens (male sex hormones) due to the sex cord-stromal tumor, leading to the observed clinical findings. A thorough understanding of the hormonal profile and the patient's clinical presentation is crucial for making an accurate diagnosis and appropriate management.